Semiconductor device and electronic appliance

ABSTRACT

The amplitude voltage of a signal input to a level shifter can be increased and then output by the level shifter circuit. Specifically, the amplitude voltage of the signal input to the level shifter can be increased to be output. This decreases the amplitude voltage of a circuit (a shift register circuit, a decoder circuit, or the like) which outputs the signal input to the level shifter. Consequently, power consumption of the circuit can be reduced. Alternatively, a voltage applied to a transistor included in the circuit can be reduced. This can suppress degradation of the transistor or damage to the transistor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/879,610, filed Sep. 10, 2010, now allowed, which claims the benefitof a foreign priority application filed in Japan as Serial No.2009-214848 on Sep. 16, 2009, both of which are incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a drivingmethod thereof. In particular, the present invention relates to asemiconductor device, a display device, a liquid crystal display device,or a light-emitting device which includes a driver circuit formed over asubstrate over which a pixel portion is formed; or the driving methodthereof. Alternatively, the present invention relates to an electronicappliance including the semiconductor device, the display device, theliquid crystal display device, or the light-emitting device.

2. Description of the Related Art

In recent years, large display devices such as liquid crystaltelevisions have been actively developed. In particular, a technique toform, using a transistor including a non-single-crystal semiconductor, adriver circuit such as a gate driver circuit over a substrate over whicha pixel portion is formed has actively developed because the techniquegreatly contributes to the reduction in manufacturing cost and theimprovement in reliability (see Patent Document 1 for example).

REFERENCE

-   [Patent Document 1] Japanese Published Patent Application No.    2004-78172

SUMMARY OF THE INVENTION

However, the amplitude voltage of a clock signal input to a shiftregister operates at the same amplitude as a gate signal (also referredto as a scan signal or a selection signal) output to, in the case of ascan line driver circuit, a scan line. The amplitude voltage of a clocksignal needs to be low for the low power consumption of a drivercircuit.

In view of the above problem, an object of one embodiment of the presentinvention is to reduce the drive voltage of a driver circuit and achievethe low power consumption of the driver circuit.

One embodiment of the present invention is a semiconductor deviceincluding a first transistor, a second transistor, a third transistor, afourth transistor, a fifth transistor, and a sixth transistor. A firstterminal of the first transistor is electrically connected to a firstwiring. A second terminal of the first transistor is electricallyconnected to a second wiring. A first terminal of the second transistoris electrically connected to a third wiring. A second terminal of thesecond transistor is electrically connected to the second wiring. Afirst terminal of the third transistor is electrically connected to thefirst wiring. A second terminal of the third transistor is electricallyconnected to a gate of the first transistor. A gate of the thirdtransistor is electrically connected to a fourth wiring. A firstterminal of the fourth transistor is electrically connected to the thirdwiring. A second terminal of the fourth transistor is electricallyconnected to the gate of the first transistor. A gate of the fourthtransistor is electrically connected to a gate of the second transistor.A first terminal of the fifth transistor is electrically connected to afifth wiring. A second terminal of the fifth transistor is electricallyconnected to the gate of the second transistor. A gate of the fifthtransistor is electrically connected to a sixth wiring. A first terminalof the sixth transistor is electrically connected to the third wiring. Asecond terminal of the sixth transistor is electrically connected to thegate of the second transistor. A gate of the sixth transistor iselectrically connected to the fourth wiring.

One embodiment of the present invention can be a semiconductor device inwhich a first signal is input to the fourth wiring, a second signal isoutput from the second wiring, and the amplitude voltage of the secondsignal is higher than that of the first signal.

One embodiment of the present invention can be a semiconductor device inwhich the first signal is a digital signal, the second signal is adigital signal, the second signal is high when the first signal is high,and the second signal is low when the first signal is low.

One embodiment of the present invention can be a semiconductor device inwhich the fourth wiring is electrically connected to a shift registercircuit.

Note that size, the thickness of layers, or regions in the drawings aresometimes exaggerated for simplicity. Therefore, the present inventionis not limited to such scales.

Note that the drawings are schematic views showing ideal examples, andthe present invention is not limited to shape or value shown in thedrawings. For example, the drawings can include the following:variations in shape due to a manufacturing technique or dimensionaldeviation; or variations in signal, voltage, or current due to noise ordifference in timing.

Technical terms are often used in order to describe a specificembodiment or the like. Note that one embodiment of the presentinvention is not construed as being limited by the technical terms.

Note that terms which are not defined (including terms used for scienceand technology, such as technical terms or academic parlance) can beused as the terms which have meaning equal to general meaning that anordinary person skilled in the art understands. It is preferable thatterms defined by dictionaries or the like be construed as consistentmeaning with the background of related art.

One embodiment of the present invention can reduce the drive voltage ofa driver circuit and achieve low power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of the circuit diagram of a semiconductor devicein Embodiment 1.

FIG. 2 is an example of the diagram showing the operation of thesemiconductor device in Embodiment 1.

FIGS. 3A and 3B are each an example of the schematic view for describingthe operation of the semiconductor device in Embodiment 1.

FIGS. 4A and 4B are each an example of the schematic view for describingthe operation of the semiconductor device in Embodiment 1.

FIGS. 5A and 5B are each an example of the circuit diagram of thesemiconductor device in Embodiment 1.

FIGS. 6A and 6B are each an example of the circuit diagram of thesemiconductor device in Embodiment 1.

FIGS. 7A and 7B are each an example of the circuit diagram of thesemiconductor device in Embodiment 1.

FIGS. 8A and 8B are each an example of the circuit diagram of thesemiconductor device in Embodiment 1.

FIGS. 9A and 9B are each an example of the circuit diagram of thesemiconductor device in Embodiment 1.

FIGS. 10A and 10B are each an example of the circuit diagram of thesemiconductor device in Embodiment 1.

FIG. 11 is an example of the circuit diagram of a semiconductor devicein Embodiment 2.

FIG. 12 is an example of the timing chart for describing the operationof the semiconductor device in Embodiment 2.

FIGS. 13A to 13C are each an example of the timing chart for describingthe operation of the semiconductor device in Embodiment 2.

FIG. 14 is an example of the timing chart for describing the operationof the semiconductor device in Embodiment 2.

FIG. 15 is an example of the circuit diagram of the semiconductor devicein Embodiment 2.

FIG. 16 is an example of the timing chart for describing the operationof the semiconductor device in Embodiment 2.

FIGS. 17A to 17D are each an example of the block diagram of a displaydevice in Embodiment 3, and FIG. 17E is an example of the circuitdiagram of a pixel in Embodiment 3.

FIG. 18A is an example of the circuit diagram of a semiconductor devicein Embodiment 4, FIG. 18B is an example of the timing chart fordescribing the operation of the semiconductor device in Embodiment 4,and FIGS. 18C and 18D are each an example of the block diagram of adisplay in Embodiment 4.

FIGS. 19A to 19C are each an example of the cross-sectional view of asemiconductor device in Embodiment 5.

FIG. 20A is an example of the top view of a display device in Embodiment6, and FIGS. 20B and 20C are each an example of the cross-sectional viewof the display device in Embodiment 6.

FIGS. 21A to 21E are each an example of the view showing a manufacturingprocess of a semiconductor device in Embodiment 7.

FIGS. 22A to 22H are each an example of the view showing an electronicappliance in Embodiment 8.

FIGS. 23A to 23H are each an example of the diagram showing anelectronic appliance in Embodiment 8.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments will be described with reference to drawings.However, the embodiments can be implemented with various modes. It willbe readily appreciated by those skilled in the art that modes anddetails can be changed in various ways without departing from the spiritand scope of the present invention. Therefore, this invention is notinterpreted as being limited to the description of the embodimentsbelow. Note that in structures of the invention described below, thesame portions or portions having similar functions are denoted by thesame reference numerals, and description thereof is not repeated.

Note that what is described (or part thereof) in one embodiment can beapplied to, combined with, or exchanged with another content in the sameembodiment and/or what is described (or part thereof) in anotherembodiment or other embodiments.

Note that terms such as “first”, “second”, “third”, and the like areused for distinguishing various elements, members, regions, layers, andareas from others. Therefore, the terms such as “first”, “second”,“third”, and the like do not limit the number of the elements, members,regions, layers, areas, or the like. Further, for example, “first” canbe replaced with “second”, “third”, or the like.

Embodiment 1

In this embodiment, an example of a semiconductor device and an exampleof the driving method of the semiconductor device will be described. Inparticular, an example of a level shifter circuit and an example of thedriving method of the level shifter circuit will be described.

First, an example of a semiconductor device in this embodiment will bedescribed.

FIG. 1 shows an example of a semiconductor device. A circuit 100includes a circuit 110 and a circuit 120. The circuit 110 is connectedto a wiring 11, a wiring 13, a wiring 14, a wiring 16, and a circuit120. The circuit 120 is connected to the wiring 11, a wiring 12, awiring 15, the wiring 16, and the circuit 110. However, one example ofthis embodiment is not limited to this. For example, the circuit 100,the circuit 110, and the circuit 120 can be connected to various wiringsaccording to its configuration.

The circuit 110 includes a transistor 111 and a transistor 112. Thecircuit 120 includes a transistor 121, a transistor 122, a transistor123, and a transistor 124. A first terminal of the transistor 121 isconnected to the wiring 15. A second terminal of the transistor 121 isconnected to the wiring 12. A first terminal of the transistor 122 isconnected to the wiring 16. A second terminal of the transistor 122 isconnected to the wiring 12. A first terminal of the transistor 123 isconnected to the wiring 15. A second terminal of the transistor 123 isconnected to a gate of the transistor 121. A gate of the transistor 123is connected to the wiring 11. A first terminal of the transistor 124 isconnected to the wiring 16. A second terminal of the transistor 124 isconnected to the gate of the transistor 121. A gate of the transistor124 is connected to a gate of the transistor 122. A first terminal ofthe transistor 111 is connected to the wiring 14. A second terminal ofthe transistor 111 is connected to the gate of the transistor 122. Agate of the transistor 111 is connected to the wiring 13. A firstterminal of the transistor 112 is connected to the wiring 16. A secondterminal of the transistor 112 is connected to the gate of thetransistor 122. A gate of the transistor 112 is connected to the wiring11.

Note that the connecting point of the second terminal of the transistor111, the second terminal of the transistor 112, the gate of thetransistor 122, and the gate of the transistor 124 is referred to as anode A. The connecting point of the gate of the transistor 121, thesecond terminal of the transistor 123, and the second terminal of thetransistor 124 is referred to as a node B.

Note that the transistor 111, the transistor 112, and the transistors121 to 124 are re-channel transistors. N-channel transistors are turnedon when a potential difference between the gate and the source getshigher than the threshold voltage. Thus, the semiconductor device inthis embodiment can be formed using a transistor including an amorphoussemiconductor, a microcrystalline semiconductor, an oxide semiconductor,an organic semiconductor, or the like. Preferably, the semiconductordevice in this embodiment is formed using a transistor including anoxide semiconductor, in particular. This is because the mobility of thetransistor can be increased by using an oxide semiconductor for asemiconductor layer. Thus, the semiconductor device in this embodimentcan be easily applied to a high-resolution display device or a largedisplay device. However, one example of this embodiment is not limitedto this. For example, all of the transistor 111, the transistor 112, andthe transistors 121 to 124 can be p-channel transistors. P-channeltransistors are turned on when a potential difference between the gateand the source gets lower than the threshold voltage.

Note that a thin film transistor is an element having at least threeterminals: a gate, a drain, and a source. In addition, a thin filmtransistor has a channel region between the drain (drain region or drainelectrode) and the source (source region or source electrode) and canconduct current through the drain, the channel region, and the source.Here, the source and the drain of the transistor change depending on thestructure, the operating condition, and the like of the transistor, andthus it is difficult to define which is a source or a drain. Therefore,a portion functioning as a source or a drain is not called a source or adrain in some cases. In that case, one of a source and a drain might bereferred to as a first terminal, a first electrode, or a first region,and the other one of the source and the drain might be referred to as asecond terminal, a second electrode, or a second region, for example.

Note that an explicit description “X and Y are connected” indicates thecase where X and Y are electrically connected, the case where X and Yare connected in terms of the function, the case where X and Y aredirectly connected, or the like. Here, each of X and Y denotes an object(e.g., a device, an element, a circuit, a wiring, an electrode, aterminal, a conductive film, a layer, or the like). Therefore, such adescription is not limited to a predetermined connection relation, e.g.connection relation shown in a drawing or text, and includes connectionrelation other than connection relation shown in a drawing or text.

A voltage VDD1 is input to the wiring 14. The voltage VDD1 has aconstant value and has a higher value than the ground voltage.Therefore, the wiring 14 serves as a power supply line or a positivepower supply line. A voltage VDD2 is input to the wiring 15. The voltageVDD2 has a constant value and has a higher value than the voltage VDD1.Therefore, the wiring 15 serves as a power supply line or a positivepower supply line. A voltage VSS is input to the wiring 16. The voltageVSS has a constant value and has a lower value than the voltage VDD1.Therefore, the wiring 16 serves as a power supply line or a negativepower supply line. However, one example of this embodiment is notlimited to this. For example, a signal can be input to the wiring 14,the wiring 15 and/or the wiring 16. In such a case, the wiring 14, thewiring 15 and/or the wiring 16 can serve as a signal line. For anotherexample, the voltage VSS can be approximately the same as the groundvoltage. Therefore, the wiring 16 can serve as a ground line or aground.

A signal IN1 is input to the wiring 11. The signal IN1 is a digitalsignal. In addition, the potential of the signal IN1 at a high level isapproximately VDD1, and the potential of the signal IN1 at a low levelis approximately VSS. Therefore, the wiring 11 serves as a signal line.A signal IN2 is input to the wiring 13. The signal IN2 is a digitalsignal. In addition, the potential of the signal IN2 at a high level isapproximately VDD1, and the potential of the signal IN2 at a low levelis approximately VSS. Therefore, the wiring 13 serves as a signal line.However, one example of this embodiment is not limited to this. Forexample, a voltage (e.g., the voltage VDD1 or the voltage VDD2) can beinput to the wiring 13. Thus, the signal IN2 can be omitted, therebyreducing the number of signals and wirings and reducing powerconsumption.

A signal OUT is output from the wiring 12. The signal OUT is a digitalsignal and is the output signal of the circuit 100. In addition, thepotential of the signal OUT at a high level is approximately VDD2, andthe potential of the signal OUT at a low level is approximately VSS,that is, the amplitude voltage of the signal OUT is higher than that ofthe signal IN1. Therefore, the wiring 12 serves as a signal line.

Next, an example of the operation of the semiconductor device in thisembodiment will be described.

FIG. 2 is a diagram showing the operation of the semiconductor device inthis embodiment. The semiconductor device in this embodiment can performthe first to fourth operations by combining the signal IN1 and thesignal IN2 at a high level or low level. The first to fourth operationswill be described. However, one example of this embodiment is notlimited to this. For example, the semiconductor device in thisembodiment can perform more operations by changing the potential of thewiring 14, the wiring 15 and/or the wiring 16.

First, the first operation will be described (see FIG. 3A). In the firstoperation, the signal IN1 goes high and the signal IN2 goes low.Consequently, the transistor 111 is turned off and the transistor 112 isturned on, so that electrical continuity between the node A and thewiring 16 is established. Then, the potential of the wiring 16 (thevoltage VSS) is supplied to the node A, and thus the potential of thenode A (referred to as a potential Va) becomes approximately VSS.Consequently, the transistor 124 is turned off. At that time, thetransistor 123 is turned on, so that electrical continuity between thenode B and the wiring 15 is established. Then, the potential of thewiring 15 (e.g., the voltage VDD2) is supplied to the node B, and thusthe potential of the node B (referred to as Vb) starts to increase.After that, the potential of the node B becomes VSS+Vth121 (Vth121: thethreshold voltage of the transistor 121), and thus the transistor 121 isturned on. At that time, the transistor 122 is turned off, so thatelectrical continuity between the wiring 12 and the wiring 15 isestablished. Then, the potential of the wiring 15 (e.g., the voltageVDD2) is supplied to the wiring 12, and thus the potential of the wiring12 (the signal OUT) starts to increase. After that, the potential of thenode B and the potential of the wiring 12 keep further increasing. Then,the potential of the node B becomes a value obtained by subtracting thethreshold voltage of the transistor 123 (Vth123) from the potential ofthe gate of the transistor 123 (the voltage VDD1). Then, the transistor123 is turned off, so that electrical continuity between the wiring 15and the node B is broken. Consequently, the node B becomes floating. Atthat time, the potential of the wiring 12 keeps increasing.Consequently, the potential of the node B further increases fromVDD1+Vth123 because of parasitic capacitance which occurs between thegate and second terminal of the transistor 121. Then, the potential ofthe node B becomes VDD2+Vth121+V1 (V1: a positive number). This isso-called a bootstrap operation. Consequently, the potential of thewiring 12 can increase to VDD2. Thus, the signal OUT goes high.

Second, the second operation will be described (see FIG. 3B). In thesecond operation, the signal IN1 goes low and the signal IN2 goes high.Consequently, the transistor 111 is turned on and the transistor 112 isturned off, so that electrical continuity between the node A and thewiring 14 is established. Then, the potential of the wiring 14 (thevoltage VDD1) is supplied to the node A, and thus the potential of thenode A increases. After that, the potential of the node A becomes avalue (referred to as VDD1−Vth 111) obtained by subtracting thethreshold voltage of the transistor 111 (Vth 111) from the potential ofthe gate of the transistor 111 (the signal IN2 at a high level). Then,the transistor 111 is turned off, so that electrical continuity betweenthe wiring 14 and the node A is broken. Thus, the node A becomesfloating, and thus the potential of the node A is kept approximatelyVDD1−Vth111. Consequently, the transistor 124 is turned on. At thattime, the transistor 123 is turned off, so that electrical continuitybetween the node B and the wiring 16 is established. Then, the potentialof the wiring 16 (the voltage VSS) is supplied to the node B, and thusthe potential of the node B becomes approximately VSS. Consequently, thetransistor 121 is turned off. At that time, the transistor 122 is turnedon, so that electrical continuity between the wiring 12 and the wiring16 is established. Then, the potential of the wiring 16 (the voltageVSS) is supplied to the wiring 12, and thus the potential of the wiring12 (the signal OUT) becomes approximately VSS. Thus, the signal OUT goeslow.

Next, the third operation will be described (see FIG. 4A). In the thirdoperation, the signal IN1 goes high and the signal IN2 goes high.Consequently, the transistor 111 is turned on and the transistor 112 isturned on, so that electrical continuity between the node A and thewiring 14, and electrical continuity between the node A and the wiring16 are established. Then, the potential of the wiring 14 (the voltageVDD1) and the potential of the wiring 16 (the voltage VSS) are suppliedto the node A, and thus the potential of the node A becomes a valueintermediate between VSS and VDD1. This potential of the node A isdetermined by the current capability of the transistor 111 and thecurrent capability of the transistor 112. Here the current capability ofthe transistor 112 is higher than that of the transistor 111. Therefore,preferably, the potential of the node A is a value nearer to VSS thanVDD1. More preferably, the potential of the node A is a value lower thanVSS+Vth124 (Vth124: the threshold voltage of the transistor 124) orlower than VSS+Vth122 (Vth122: the threshold voltage of the transistor122). Consequently, the transistor 124 is turned off. At that time, thetransistor 123 is turned on, so that electrical continuity between thenode B and the wiring 15 is established. Then, the potential of thewiring 15 (e.g., the voltage VDD2) is supplied to the node B, and thusthe potential of the node B (which potential is referred to as Vb)starts to increase. After that, the potential of the node B becomesVSS+Vth121 (Vth121: the threshold voltage of the transistor 121), andthus the transistor 121 is turned on. At that time, the transistor 122is turned off, so that electrical continuity between the wiring 12 andthe wiring 15 is established. Then, the potential of the wiring 15(e.g., the voltage VDD2) is supplied to the wiring 12, and thus thepotential of the wiring 12 (the signal OUT) starts to increase. Afterthat, the potential of the node B and the potential of the wiring 12keep further increasing. Then, the potential of the node B becomes avalue obtained by subtracting the threshold voltage of the transistor123 (Vth 123) from the potential of the gate of the transistor 123 (thevoltage VDD1). Then, the transistor 123 is turned off, so thatelectrical continuity between the wiring 15 and the node B is broken.Consequently, the node B becomes floating. At that time, the potentialof the wiring 12 keeps increasing. Consequently, the potential of thenode B further increases from VDD1−Vth123 because of parasiticcapacitance which occurs between the gate and second terminal of thetransistor 121. Then, the potential of the node B becomes VDD2+Vth121+V1(V1: a positive number). This is so-called a bootstrap operation.Consequently, the potential of the wiring 12 can increase to VDD2. Thus,the signal OUT goes high.

Next, the fourth operation will be described (see FIG. 4B). In thefourth operation, the signal IN1 goes low and the signal IN2 goes low.Consequently, the transistor 111 is turned off and the transistor 112 isturned off, so that the node A becomes floating. Then, the potential ofthe node A remains at the same state as in the operation prior to thefourth operation. For example, suppose that the semiconductor deviceperforms the first operation or the third operation prior to the fourthoperation. In this case, the potential of the node A becomesapproximately VSS. Then, suppose that the semiconductor device performsthe second operation prior to the fourth operation. In this case, thepotential of the node A becomes approximately VDD1−Vth111. Here, thesemiconductor device performs the second operation prior to the fourthoperation. Consequently, the potential of the node A is thus maintainedat approximately VDD1−Vth111. Consequently, the transistor 124 is turnedon. At that time, the transistor 123 is turned off, so that electricalcontinuity between the node B and the wiring 16 is established. Then,the potential of the wiring 16 (the voltage VSS) is supplied to the nodeB, and thus the potential of the node B becomes approximately VSS.Consequently, the transistor 121 is turned off. At that time, thetransistor 122 is turned on, so that electrical continuity between thewiring 12 and the wiring 16 is established. Then, the potential of thewiring 16 (the voltage VSS) is supplied to the wiring 12, and thus thepotential of the wiring 12 (the signal OUT) becomes approximately VSS.Thus, the signal OUT goes low.

As described above, in the semiconductor device in this embodiment, theamplitude voltage of the signal IN1 can be increased to be output.Specifically, the amplitude voltage of the signal IN1 can be increasedto be output. This decreases the amplitude voltage of a circuit (a shiftregister circuit, a decoder circuit, or the like) which outputs thesignal IN1 to the semiconductor device in this embodiment. Consequently,the power consumption of the circuit can be reduced. Alternatively, avoltage applied to a transistor in the circuit can be reduced. Thissuppresses degradation of the transistor or damage to the transistor.

Alternatively, the timing of inverting the signal OUT can beapproximately the same as the timing of inverting the signal IN1. Thus,the wiring 12 does not need to have an inverter circuit or the like.This achieves the reduction in power consumption, the reduction incircuit size, or the reduction in layout area.

Alternatively, in the first operation, when the signal IN1 is high, thesignal IN2 goes low, thereby preventing flow-through current whichoccurs between the wiring 14 and the wiring 16. This reduces the powerconsumption.

Note that although the first to fourth operations have been described,the semiconductor device in this embodiment does not need to perform allthe operations. The semiconductor device in this embodiment can selectonly a necessary operation from these operations and perform theselected operation.

Next, a structure of the semiconductor device in this embodiment, whichstructure is different from that in FIG. 1 will be described.

In the semiconductor device in FIG. 1, the first terminal of thetransistor 111 can be connected to a wiring other than the wiring 14 asshown in FIGS. 5A and 5B. FIG. 5A shows an example of the semiconductordevice in which the first terminal of the transistor 111 is connected tothe wiring 15. In this structure, the voltage VDD1 can be omitted.Alternatively, a potential difference applied between the source anddrain of the transistor 111 (Vds) can be increased; thus, the rise timeof the potential of the node A can be shortened. FIG. 5B shows anexample of the semiconductor device in which the first terminal of thetransistor 111 is connected to the wiring 13. In this structure, thevoltage VDD1 can be omitted. Alternatively, the transistor 111 can bereverse-biased, so that degradation of the transistor 111 can besuppressed. However, one example of this embodiment is not limited tothis. For example, the first terminal of the transistor 111 can beconnected to a wiring to which an inverted signal of the signal IN1 isinput.

In the semiconductor devices in FIG. 1 and FIGS. 5A and 5B, the gate ofthe transistor 111 can be connected to a wiring other than the wiring 13as shown in FIGS. 6A and 6B. FIG. 6A shows an example of thesemiconductor device in which the gate of the transistor 111 isconnected to the wiring 15. In this structure, the signal 1N2 can beomitted. This reduces the power consumption. FIG. 6B shows an example ofthe semiconductor device in which the gate of the transistor 111 isconnected to the wiring 14. In this structure, the signal IN2 can beomitted. This reduces the power consumption. However, one example ofthis embodiment is not limited to this. For example, the gate of thetransistor 111 can be connected to a wiring to which an inverted signalof the signal IN1 is input.

In the semiconductor devices in FIG. 1, FIGS. 5A and 5B, and FIGS. 6Aand 6B, the first terminal of the transistor 111 can be connected to awiring other than the wiring 14, and the gate of the transistor 111 canbe connected to a wiring other than the wiring 13 as shown in FIG. 7A.FIG. 7A shows an example of the semiconductor device in which the firstterminal of the transistor 111 is connected to the wiring 13, and thegate of the transistor 111 is connected to the wiring 14. In thisstructure, the potential of the node A can be increased in the secondoperation, and the potential of the node A can be decreased in thefourth operation. Thus, the transistor 122 and the transistor 124 areturned on in the second operation, and the transistor 122 and thetransistor 124 are turned off in the fourth operation. Thus, the timeover which the transistor 122 and the transistor 124 are on can beshortened. This suppresses degradation of the transistor 122 and thetransistor 124.

In the semiconductor devices in FIG. 1, FIGS. 5A and 5B, FIGS. 6A and6B, and FIG. 7A, the first terminal of the transistor 123 can beconnected to a wiring other than the wiring 15 as shown in FIG. 7B andFIG. 8A. FIG. 7B shows an example of the semiconductor device in whichthe first terminal of the transistor 123 is connected to a wiring 13B. Asignal IN2B is input to the wiring 13B. The signal IN2B is an invertedsignal of the signal IN2. Thus, the transistor 123 can bereverse-biased, so that degradation of the transistor can be suppressed.FIG. 8A shows an example of the semiconductor device in which the firstterminal of the transistor 123 is connected to the wiring 11. In thisstructure, a potential difference applied between the source and drainof the transistor 123 (Vds) can be decreased in the second operation andthe fourth operation. Thus, degradation of the transistor 123 can besuppressed. Alternatively, the off state current of the transistor 123can be reduced, thereby reducing the power consumption. However, oneexample of this embodiment is not limited to this. For example, thefirst terminal of the transistor 123 can be connected to the wiring 14.

Note that when the first terminal of the transistor 123 is connected tothe wiring 11, the gate of the transistor 123 can be connected to awiring other than the wiring 11 as shown in FIG. 8B. FIG. 8B shows anexample of the semiconductor device in which the gate of the transistor123 is connected to the wiring 14. However, one example of thisembodiment is not limited to this. The gate of the transistor 123 can beconnected to the wiring 15, a wiring to which an inverted signal of thesignal IN2 is input, or a wiring to which a signal which is not in phasewith the signal IN2.

In the semiconductor device in FIG. 1, FIGS. 5A and 5B, FIGS. 6A and 6B,FIGS. 7A and 7B, and FIGS. 8A and 8B, a capacitor 125 can be providedbetween the gate and second terminal of the transistor 121 as shown inFIG. 9A. Thus, the potential of the node B can be further increased inthe first operation and the second operation. Therefore, a potentialdifference between the gate and source of the transistor 121 (Vgs) canbe increased, so that the rise time of the signal OUT can be shortened.

In the semiconductor device in FIG. 1, FIGS. 5A and 5B, FIGS. 6A and 6B,FIGS. 7A and 7B, FIGS. 8A and 8B, and FIG. 9A, a capacitor 126 can beprovided between the node A and the wiring 16 as shown in FIG. 9B. Thus,fluctuations of the potential of the node A, noise at the node A, or thelike can be suppressed, so that the potential of the node A can beeasily maintained. However, one example of this embodiment is notlimited to this. For example, the capacitor 126 can be connected betweenthe node A and a wiring other than the wiring 16 (e.g., the wiring 13,the wiring 14, the wiring 15, or the like). In particular, by connectingthe capacitor 126 between the node A and the wiring 13, the potential ofthe node A can be changed in synchronism with the signal IN2. Thus, thetime over which the transistor 122 and the transistor 124 are on can beshortened.

In the semiconductor devices in FIG. 1, FIGS. 5A and 5B, FIGS. 6A and6B, FIGS. 7A and 7B, FIGS. 8A and 8B, and FIGS. 9A and 9B, thetransistors can be connected to different wirings as shown in FIG. 10A.FIG. 10A shows an example of the semiconductor device in which the firstterminal of the transistor 112, the second terminal of the transistor124, and the second terminal of the transistor 122 are connected todifferent wirings. The wiring 16 is divided into a plurality of wirings:wirings 16A to 16C. The first terminal of the transistor 112, the secondterminal of the transistor 124, and the second terminal of thetransistor 122 are connected to the wiring 16A, the wiring 16B, and thewiring 16C, respectively. However, one example of this embodiment is notlimited to this. For example, also the first terminal of the transistor121 and the first terminal of the transistor 123 can be connected todifferent wirings. In this case, the wiring 15 can be divided into twowirings.

In the semiconductor devices in FIG. 1, FIGS. 5A and 5B, FIGS. 6A and6B, FIGS. 7A and 7B, FIGS. 8A and 8B, FIGS. 9A and 9B, and FIG. 10A, atransistor can be replaced with a resistor, a diode, a capacitor, or thelike as shown in FIG. 10B. FIG. 10B shows an example of thesemiconductor device in which the transistor 111 is replaced with adiode 111 d. One electrode (e.g. the anode) of the diode 111 d isconnected to the wiring 13, and the other electrode (e.g. the cathode)is connected to the node A. However, one example of this embodiment isnot limited to this. For example, the transistor 111 can be replacedwith a resistor. The resistor can be connected between the node A andany one of the wirings 13 to 15. For another example, one electrode(e.g. the anode) of the transistor 123 can be connected to the wiring11, and the other electrode (e.g. the cathode) can be replaced with adiode connected to the node B. For another example, the diode can be adiode-connected transistor.

Next, an example of the function of each circuit and an example of thefunction of each transistor will be described.

The circuit 100 has a function of increasing the amplitude voltage ofthe signal IN1. Alternatively, the circuit 100 has a function ofincreasing the potential of the signal IN1 at a high level.Alternatively, the circuit 100 has a function of inverting the signalOUT when the signal IN1 is inverted. Alternatively, the circuit 100 hasa function of setting the signal OUT high when the signal IN1 goes high.Alternatively, the circuit 100 has a function of setting the signal OUTlow when the signal IN1 goes low. Thus, the circuit 100 serves as alevel shifter circuit.

Note that by setting the voltage VDD2 smaller than the voltage VDD1, thepotential of the signal OUT at a high level can be made lower than thepotential of the signal IN1 or IN2 at a high level. In this case, thecircuit 100 has a function of decreasing the amplitude voltage of thesignal IN1.

The circuit 110 has a function of inverting the signal IN1.Alternatively the circuit 110 has a function of decreasing the potentialof the node A when the signal IN1 goes high. Alternatively, the circuit110 has a function of increasing the potential of the node A when thesignal IN1 goes low. Alternatively, the circuit 110 has a function ofsetting the node A floating. Thus, the circuit 110 serves as an invertercircuit.

The circuit 120 has a function of increasing the amplitude voltage ofthe signal IN1. Alternatively, the circuit 120 has a function ofincreasing the potential of the signal IN1 at a high level.Alternatively, the circuit 120 has a function of inverting the signalOUT when the signal IN1 is inverted. Alternatively, the circuit 120 hasa function of setting the signal OUT high when the signal IN1 goes high.Alternatively, the circuit 120 has a function of setting the signal OUTlow when the signal IN1 goes low. Thus, the circuit 120 serves as alevel shifter circuit.

The transistor 111 has a function of controlling electrical continuitybetween the wiring 14 and the node A. Alternatively, the transistor 111has a function of controlling the timing of supplying the potential ofthe wiring 14 to the node A. Alternatively, the transistor 111 has afunction of controlling the timing of increasing the potential of thenode A. Alternatively, the transistor 111 has a function of controllingthe timing of setting the node A floating. Thus, the transistor 111serves as a switch.

The transistor 112 has a function of controlling electrical continuitybetween the wiring 16 and the node A. Alternatively, the transistor 112has a function of controlling the timing of supplying the potential ofthe wiring 16 to the node A. Alternatively, the transistor 112 has afunction of controlling the timing of decreasing the potential of thenode A. Thus, the transistor 112 serves as a switch.

The transistor 121 has a function of controlling electrical continuitybetween the wiring 15 and the wiring 12. Alternatively, the transistor121 has a function of controlling the timing of supplying the potentialof the wiring 15 to the wiring 12. Alternatively, the transistor 121 hasa function of controlling the timing of increasing the potential of thewiring 12. Alternatively, the transistor 121 has a function ofcontrolling the timing of performing a bootstrap operation.Alternatively, the transistor 121 has a function of controlling thetiming of increasing the potential of the node B. Thus, the transistor121 serves as a switch.

The transistor 122 has a function of controlling electrical continuitybetween the wiring 16 and the wiring 12. Alternatively, the transistor122 has a function of controlling the timing of supplying the potentialof the wiring 16 to the wiring 12. Alternatively, the transistor 122 hasa function of controlling the timing of decreasing the potential of thewiring 12. Thus, the transistor 122 serves as a switch.

The transistor 123 has a function of controlling electrical continuitybetween the wiring 15 and the node B. Alternatively, the transistor 123has a function of controlling the timing of supplying the potential ofthe wiring 14 to the node B. Alternatively, the transistor 123 has afunction of controlling the timing of increasing the potential of thenode B. Alternatively, transistor 123 has a function of controlling thetiming of setting the node B floating. Thus, the transistor 123 servesas a switch.

The transistor 124 has a function of controlling electrical continuitybetween the wiring 16 and the node B. Alternatively, the transistor 124has a function of controlling the timing of supplying the potential ofthe wiring 16 to the node B. Alternatively, the transistor 124 has afunction of controlling the timing of decreasing the potential of thenode B. Thus, the transistor 124 serves as a switch.

Next, an example of the channel width of each transistor will bedescribed.

The channel width of the transistor 121 is preferably larger than thatof the transistor 111, the transistor 112, and the transistors 122 to124. In other words, the channel width of the transistor 121 ispreferably the largest among the channel widths of the transistors inthe circuit 100. This is because the transistor 121 drives the wiring 12and thus needs a large drive capability. Note that the channel width ofthe transistor 121 is preferably twice to 10 times as large as that ofthe transistor 123. More preferably, the channel width of the transistor121 is three to eight times as large as that of the transistor 123. Muchmore preferably, the channel width of the transistor 121 is four to sixtimes as large as that of the transistor 123.

The channel width of the transistor 122 is preferably larger than thatof the transistor 111, the transistor 112, the transistors 123, and thetransistor 124. This is because the transistor 122 drives the wiring 12and thus needs a large drive capability. Note that the channel width ofthe transistor 122 is preferably twice to 30 times as large as that ofthe transistor 124. More preferably, the channel width of the transistor122 is 4 to 15 times as large as that of the transistor 124. Much morepreferably, the channel width of the transistor 121 is 6 to 10 times aslarge as that of the transistor 124.

Note that the channel width of the transistor 122 can be larger thanthat of the transistor 121.

The channel width of the transistor 123 is preferably larger than thatof the transistor 124. This is in order for the potential of the node Bto increase even when the transistor 123 and the transistor 124 areturned on at the same time in the first operation and the thirdoperation because of difference in timing. Note that the channel widthof the transistor 123 is preferably 1.5 to 10 times as large as that ofthe transistor 124. More preferably, the channel width of the transistor123 is twice to eight times as large as that of the transistor 124. Muchmore preferably, the channel width of the transistor 123 is 2.5 to 5times as large as that of the transistor 124.

Note that the current capability of a transistor can be controlled bythe channel width of the transistor. Specifically, the larger thechannel width of the transistor, the more the current capability of thetransistor is improved. However, a factor which controls the currentcapability of the transistor is not limited to the channel width of thetransistor. For example, the current capability can be controlled by thechannel length of the transistor or a potential difference between thegate and source of the transistor (Vgs). Specifically, the smaller thechannel length of the transistor, the more the current capability of thetransistor is improved. In addition, the larger the potential differencebetween the gate and source of the transistor (Vgs), the more thecurrent capability of the transistor is improved. Additionally, thecurrent capability can be decreased by a multi-gate transistor.

As described above, there is a plurality of methods of controlling thecurrent capability of a transistor. Consequently, in the case where amethod of controlling a channel width is shown below as an example ofthe method of controlling the current capability of the transistor, sucha channel width can be referred to as a channel length or a potentialdifference between the gate and source of a transistor (Vgs).

Embodiment 2

In this embodiment, an example of a semiconductor device and an exampleof a driving method of the semiconductor device will be described. Thesemiconductor device in this embodiment includes the semiconductordevice in Embodiment 1.

First, an example of the semiconductor device in this embodiment will bedescribed.

FIG. 11 shows an example of the semiconductor device in this embodiment.A semiconductor device in FIG. 11 includes a circuit 300, a circuit 400,and a circuit 500. The circuit 400 includes circuits 401_1 to 401 _(—) m(m is a natural number). In addition, the semiconductor device inEmbodiment 1 can be used as each of the circuits 401_1 to 401 _(—) m. InFIG. 11, the semiconductor device in FIG. 1 can be used as each of thecircuits 401_1 to 401 _(—) m. The circuit 500 includes a circuit 501 anda circuit 502.

The circuit 300 is connected to wirings 21_1 to 21 _(—) m, a wiring 23,wirings 24_1 to 24_4, a wiring 25, and a wiring 27. The circuit 400 isconnected to the wirings 21_1 to 21 _(—) m, wirings 22_1 to 22 _(—) m,the wirings 24_1 to 24_4, the wiring 25, a wiring 26, and the wiring 27.The circuit 401 _(—) i (i is any one of 1 to m) is connected to thewiring 21 _(—) i, the wiring 22 _(—) i, any one of the wirings 24_1 to24_4, the wiring 25, the wiring 26, and the wiring 27. Further, in thecircuit 401 _(—) i, the wiring 11, the wiring 12, the wiring 13, thewiring 14, the wiring 15, and the wiring 16 are connected to the wiring21 _(—) i, the wiring 22 _(—) i, any one of the wirings 24_1 to 24_4,the wiring 25, the wiring 26, and the wiring 27, respectively. Thecircuit 500 is connected to the wiring 23, the wirings 24_1 to 24_4, thewiring 25, the wiring 26, and the wiring 27. The circuit 501 isconnected to the wiring 23 and the wirings 24_1 to 24_4. The circuit 502is connected to the wiring 25, the wiring 26, and the wiring 27.

Note that when it is assumed that the circuit 401 _(—) i is connected tothe wiring 24_1, the circuit 401 _(—) i+1, the circuit 401 _(—) i+2, andthe circuit 401 _(—) i+3 are often connected to the wiring 242, thewiring 24_3, and the wiring 24_4, respectively. Alternatively, thecircuit 401 _(—) i−3, the circuit 401 _(—) i−2, and the circuit 401 _(—)i−1 are often connected to the wiring 242, the wiring 24_3, and thewiring 24_4, respectively.

Note that the circuit 401 _(—) i is preferably connected to one of thewirings 24_1 to 24_4, whose potential goes low in a period in which thesignal SOUTi goes high. Thus, a period in which the transistor 111 andthe transistor 112 are turned on at the same time can be omitted. Thisreduces the power consumption.

The circuit 500 has a function of controlling the timing of supplying asignal, a voltage, or the like to the circuits 300 and 400. Further, thecircuit 500 has a function of controlling the timing of when the circuit300 and the circuit 400 operate. In other words, the circuit 500 servesas a controller.

The circuit 501 has a function of controlling the timing of outputting asignal SP, a signal CK1, a signal CK2, a signal CK3, and a signal CK4 tothe wiring 23, the wiring 24_1, the wiring 242, the wiring 24_3, and thewiring 24_4, respectively. In other words, the circuit 501 serves as asignal-generating circuit (also referred to as a timing generator).Therefore, the circuit 501 can include a switch, a diode, a transistor,an oscillator circuit, a clocked generator, a PLL circuit and/or afrequency divider circuit.

The signal SP, the signal CK1, the signal CK2, the signal CK3, and thesignal CK4 are often digital signals as shown in FIG. 12. The potentialof these signals at a high level is approximately VDD1, and thepotential of these signals at a low level is approximately VSS. Inaddition the signal SP serves as a start pulse (also referred to as ahorizontal synchronizing signal or a vertical synchronizing signal).Therefore, the wiring 23 serves as a signal line (also referred to as astart signal line). The signals CK1 to CK4 each function as a clocksignal. Each of the signals CK1 to CK4 is out of phase with thesubsequent clock signal by ¼ cycle (90°). Therefore, the wiring 24_1 to24_4 serve as clock signal lines (also referred to as signal lines).

Note that the signals CK1 to CK4 are balanced signals as shown in FIG.12. A balanced signal is a signal whose period in which the signal ishigh and whose period in which the signal is low in one cycle haveapproximately the same length. However, one example of this embodimentis not limited to this. For example, the signals CK1 to CK4 can beunbalanced signals as shown in FIG. 13A. An unbalanced signal is asignal whose period in which the signal is high and whose period inwhich the signal is low in one cycle have different lengths. Here, theterm “different” is used in consideration of the case except the casewhere the length of the periods is approximately equal to each other.

Note that a single-phase clock signal can be used for the semiconductordevice in this embodiment as shown in FIGS. 13B and 13C. In this casealso, a clock signal can be either a balanced signal as shown in FIG.13B or an unbalanced signal as shown in FIG. 13C. However, one exampleof this embodiment is not limited to this. For example, a three-phaseclock signal or a five- or more phase clock signal can be used for thesemiconductor device in this embodiment.

The circuit 502 has a function of outputting the voltage VDD1, thevoltage VDD2, and the voltage VSS to the wiring 25, the wiring 26, andthe wiring 27, respectively. In other words, the circuit 502 serves as apower supply circuit (also referred to as a regulator). Therefore, thewiring 25 serves as a power supply line or a positive power supply line.The wiring 27 serves as a power supply line, a negative power supplyline, a ground line. Therefore, the circuit 502 can include a switch, atransistor, a capacitor, a coil, a diode, a regulator, a DCDC converterand/or a booster circuit.

Note that the circuit 500, the circuit 501, and the circuit 502 cansupply various signals or voltages to the circuit 300 and the circuit400 according to the configuration of the circuit 300 and the circuit400.

The circuit 300 has a function of controlling the timing of outputtingsignals SOUT1 to SOUTm according to a signal and a voltage from thecircuit 500 (e.g., the signal SP, the signals CK1 to CK4, the voltageVDD1, and the voltage VSS). The signals SOUT1 to SOUTm are often digitalsignals, and the potential of the signals SOUT1 to SOUTm at a high levelis approximately VDD1, and the potential of the signals SOUT1 to SOUTmat a low level is approximately VSS. In addition, the circuit 300 has afunction of setting sequentially the signals SOUT1 to SOUTm high. Inother words, the circuit 300 serves as a shift register circuit.However, one example of this embodiment is not limited to this. Forexample, the circuit 300 can have the function of setting the signalsSOUT1 to SOUTm high in a predetermined order. Therefore, the circuit 300can serve as a decoder circuit.

Note that the signals SOUT1 to SOUTm are input to the circuit 400 viathe wirings 21_1 to 21 _(—) m, respectively. For example, the signalSOUTi is input to the circuit 401 _(—) i via the wiring 21 _(—) i.Therefore, the wirings 21_1 to 21 _(—) m each serve as a signal line.

Note that in a timing chart in FIG. 12, part of a period in which thesignal SOUTi is high and part of a period in which the signal SOUTi−1 ishigh overlap with each other. Further, part of a period in which thesignal SOUTi is high and part of a period in which the signal SOUTi+1 ishigh overlap with each other. Therefore, a period in which the signalsSOUT1 to SOUTm are high can be longer. Thus, the drive frequency of thecircuit 300 can be reduced, thereby reducing the power consumption.However, one example of this embodiment is not limited to this. Forexample, it is possible for periods in which the signals SOUT1 to SOUTmare high not to overlap with each other.

The circuit 400 has a function of controlling the timing of outputtingsignals BOUT1 to BOUTm according to a signal from the circuit 300 (e.g.,the signals SOUT1 to SOUTm), and a signal and voltage from the circuit500 (e.g., the signals CK1 to CK4, the voltage VDD1, the voltage VDD2,and the voltage VSS). The signals BOUT1 to BOUTm are often digitalsignals, and the potential of the signals BOUT1 to BOUTm at a high levelis approximately VDD2, and the potential of the BOUT1 to BOUTm at a lowlevel is approximately VSS. In addition, the timing of when the signalsBOUT1 to BOUTm are inverted is approximately the same as the timing ofwhen the signals SOUT1 to SOUTm are inverted. In other words, thecircuit 400 has a function of increasing the amplitude voltage of thesignals SOUT1 to SOUTm.

Next, an example of the operation of the semiconductor device in thisembodiment will be described.

FIG. 14 is an example of the timing chart of the circuit 401 _(—) i.FIG. 14 shows the signal SOUTi, the signal CK, the potential of the nodeA of the circuit 401 _(—) i, the potential of the node B of the circuit401 _(—) i, and the signal BOUTi. The signal CK is any one of the signalCK1 to CK4. The signal CK is a signal of the signal CK1 to CK4, whichgoes low when the signal SOUTi goes high. In addition, the timing chartin FIG. 14 includes a period Ta, a period Tb, and a period Tc. In thetiming chart in FIG. 14, there are, in addition to the period Ta, theperiod Tb and the period Tc which are provided in order.

Note that the signal SOUTi corresponds to the signal IN1 in FIG. 2. Thesignal CK corresponds to the signal IN2 in FIG. 2. The signal BOUTicorresponds to the signal OUT in FIG. 2.

First, in the period Ta, the signal SOUTi goes high, and the signal CKgoes low. Then, the circuit 400 _(—) i performs the first operation.Accordingly, the signal BOUTi goes high. This raises the potential ofthe signal SOUTi at a high level from VDD1 to VDD2.

Next, in the period Tb, the signal SOUTi goes low, and the signal CKgoes high. Then, the circuit 400 _(—) i performs the second operation.Consequently, the signal BOUTi goes low.

Next, in the period Tc, the signal SOUTi remains low, and the signal CKgoes low. Then, the circuit 400 _(—) i performs the fourth operation.Further, since the previous period of the period Tc is the period Tb,the potential Va remains VDD1−Vth111. Consequently, the signal BOUTiremains low.

As described above, the semiconductor device in this embodiment canamplify the amplitude voltage of an output signal of the circuit 300 andthen output the signal. This decreases the amplitude voltage of thecircuit 300. Therefore, the power consumption of the circuit 300 can bereduced.

Alternatively, the circuits 401_1 to 401 _(—) m each often perform anyof the first operation, the second operation, and the fourth operation.Therefore, there is no period in which the transistor 111 and thetransistor 112 are turned on at the same time, and the power consumptionis thus reduced.

Next, an example of the circuit 300 will be described.

FIG. 15 shows an example of the circuit 300. The circuit 300 includescircuits 310_1 to 310 _(—) m. The circuit 310 _(—) i is connected to thewiring 21 _(—) i, the wiring 21 _(—) i−1, the wiring 21 _(—) i+2, threeof the wirings 24_1 to 24_4, the wiring 25, and the wiring 27. However,the circuit 310_1 is often connected to the wiring 23 instead of thewiring 21 _(—) i−1.

Each of the circuits 310_1 to 310 _(—) m includes a transistor 311, atransistor 312, a transistor 313, a transistor 314, a transistor 315, atransistor 316, a transistor 317, a transistor 318, and a transistor319. A first terminal of the transistor 311 is connected to a wiring 33,and a second terminal of the transistor 311 is connected to a wiring 32.A first terminal of the transistor 312 is connected to a wiring 37, asecond terminal of the transistor 312 is connected to the wiring 32, anda gate of the transistor 312 is connected to a wiring 35. A firstterminal of the transistor 313 is connected to the wiring 37, and asecond terminal of the transistor 313 is connected to the wiring 32. Afirst terminal of the transistor 314 is connected to the wiring 37, asecond terminal of the transistor 314 is connected to a gate of thetransistor 311, and a gate of the transistor 314 is connected to a gateof the transistor 313. A first terminal of the transistor 315 isconnected to a wiring 36, a second terminal of the transistor 315 isconnected to the gate of the transistor 311, and a gate of thetransistor 315 is connected to a wiring 31. A first terminal of thetransistor 316 is connected to the wiring 36, a second terminal of thetransistor 316 is connected to the gate of the transistor 313, and agate of the transistor 316 is connected to a wiring 38. A first terminalof the transistor 317 is connected to the wiring 36, and a gate of thetransistor 317 is connected to the wiring 35. A first terminal of thetransistor 318 is connected to the second terminal of the transistor317, a second terminal of the transistor 318 is connected to the gate ofthe transistor 313, and a gate of the transistor 318 is connected to awiring 34. A first terminal of the transistor 319 is connected to thewiring 37, a second terminal of the transistor 319 is connected to thegate of the transistor 313, and a gate of the transistor 319 isconnected to the wiring 31.

Note that a connecting point of the gate of the transistor 311, thesecond terminal of the transistor 314, and the second terminal of thetransistor 315 is referred to as a node C. A connecting point of thegate of the transistor 313, the gate of the transistor 314, the secondterminal of the transistor 316, the second terminal of the transistor318, and the second terminal of the transistor 319 is referred to as anode D.

Note that the transistors 311 to 319 are n-channel transistors. Thus,all of the semiconductor devices in this embodiment can be n-channeltransistors. However, one example of this embodiment is not limited tothis. For example, all of the transistors 311 to 319 can be p-channeltransistors.

Note that in the circuit 310 _(—) i, the wiring 31 is connected to thewiring 21 _(—) i−1. The wiring 32 is connected to the wiring 21 _(—) i.The wirings 33 to 35 are connected to three wirings selected from thewirings 24_1 to 24_4. For example, when the wiring 33 is connected tothe wiring 24_1, the wiring 34 is connected to the wiring 242, and thewiring 35 is connected to the wiring 24_3. The wiring 36 is connected tothe wiring 25. The wiring 37 is connected to the wiring 27. The wiring38 is connected to the wiring 21 _(—) i+2. However, in the circuit310_1, the wiring 31 is connected to the wiring 23.

Next, an example of the operation of the circuit 300 will be described.

FIG. 16 shows an example of the timing chart which can be used for thecircuit 310 _(—) i. The timing chart in FIG. 16 shows a signal IN33, asignal IN34, a signal IN35, the signal SOUTi−1, the signal SOUTi+1, thepotential of the node C (potential Vc), the potential of the node D(potential Vd), and the signal SOUTi. In addition, the timing chart inFIG. 16 includes periods T1 to T9. The periods T5 to T9 are provided inorder, and the periods T1 to T4 are repeatedly provided in order inother periods than the periods T5 to T9.

First, in the period T1, the signal SOUTi goes low, the signal SOUTi+2goes low, the signal IN33 goes low, the signal IN34 goes high, and thesignal IN35 goes high. Consequently, the transistor 316 is turned off,the transistor 317 is turned on, the transistor 318 is turned on, andthe transistor 319 is turned off, so that electrical continuity betweenthe node D and the wiring 36 is established. Then, the potential of thewiring 36 (e.g., the voltage VDD) is supplied to the node D, and thusthe potential of the node D increases. Consequently, the transistor 314is turned on. At that time, the transistor 315 is turned off, so thatelectrical continuity between the node C and the wiring 37 isestablished. Then, the potential of the wiring 37 (e.g., the voltageVSS) is supplied to the node C, and thus the potential of the node Cbecomes approximately VSS. Consequently, the transistor 311 is turnedoff. At that time, the transistor 312 and the transistor 313 are turnedon, so that electrical continuity between the wiring 32 and the wiring37 is established. Then, the potential of the wiring 37 (e.g., thevoltage VSS) is supplied to the wiring 32, and thus the potential of thewiring 32 becomes approximately VSS. Consequently, the signal SOUTi goeslow.

Next, in the period T2, the signal IN34 goes low, which is differentfrom in the period T1. Consequently, the transistor 318 is turned off,so that electrical continuity between the wiring 36 and the node D isbroken. Then, the node D becomes floating, and the potential of the nodeD thus maintains the same potential as that in the period T1.

Next, in the period T3, the signal IN33 goes high and the signal IN35goes low, which is different from in the period T2. Consequently, thetransistor 317 and the transistor 312 are turned off.

Next, in the period T4, the signal IN34 goes high, which is differentfrom in the period T3. Consequently, the transistor 318 is turned on.

Next, in the period T5, the signal SOUTi goes high, the signal SOUTi+2goes low, the signal IN33 goes low, the signal IN34 goes low, and thesignal IN35 goes high. Consequently, the transistor 316 is turned off,the transistor 317 is turned on, the transistor 318 is turned off, andthe transistor 319 is turned on, so that electrical continuity betweenthe wiring 37 and the node D is established. Then, the potential of thewiring 37 (the voltage VSS) is supplied to the node D, and thus thepotential of the node D becomes approximately VSS. Consequently, thetransistor 314 is turned off. At that time, the transistor 315 is turnedon, so that electrical continuity between the node C and the wiring 36is established. Then, the potential of the wiring 36 is supplied to thenode C, and the potential of the node C starts to increase. Then, thepotential of the node C becomes the sum of the potential of the wiring32 (VSS) and the threshold voltage of the transistor 311 (Vth311)(VSS+Vth311). Consequently, the transistor 311 is turned on. At thattime, the transistor 312 is turned on and the transistor 313 is turnedoff, so that electrical continuity between the wiring 32 and the wiring37 and electrical continuity between the wiring 32 and the wiring 33 areestablished. Then, the potential of the wiring 37 (the voltage VSS) andthe potential of the wiring 33 (the signal IN33 at a low level) aresupplied to the wiring 32, and thus the potential of the wiring 37becomes approximately VSS. Consequently, the signal SOUTi goes low.After that, the potential of the node C keeps increasing. Then, thepotential of the node C becomes VDD1−Vth315 (Vth315 is the thresholdvoltage of the transistor 315). Consequently, the transistor 315 isturned off, and the node C becomes floating. Thus, the potential of thenode C remains VDD1−Vth315.

Next, in the period T6, the signal SOUTi−1 remains high, the signalSOUTi+2 remains low, the signal IN33 goes high, the signal IN34 remainslow, and the signal IN35 goes low. Consequently, the transistor 316remains off, the transistor 317 is turned off, the transistor 318remains off, and the transistor 319 remains on, so that electricalcontinuity between the node D and the wiring 37 remains established.Then, the potential of the wiring 37 (the voltage VSS) keeps beingsupplied to the node D, and the potential of the node D remainsapproximately VSS. Consequently, the transistor 314 remains off. At thattime, the transistor 315 remains off. Then, the node C becomes floating,so that the potential of the node C remains VDD1−Vth315. Consequently,the transistor 311 remains on. As a result, the transistor 312 and thetransistor 313 are turned off, so that electrical continuity between thewiring 32 and the wiring 33 is established. At that time, the signalIN33 goes high, and thus the potential of the wiring 32 starts toincrease. At the same time, the potential of the node C increasesbecause of a bootstrap operation. As a result, the potential of the nodeC increases to VDD1+Vth311+V1 (Vth311 is the threshold voltage of thetransistor 311). Consequently, the potential of the wiring 32 increasesto VDD1. Thus, the signal SOUTi goes high.

Next, in the period T7, the signal SOUTi−1 goes low, the signal IN34goes high, which is different from in period T6. Consequently, thetransistor 318 is turned on, and the transistor 319 is turned off. Then,the node D becomes floating, and the potential of the node D remainsapproximately VSS.

Next, in the period T8, the signal SOUTi−1 remains low, the signalSOUTi+2 goes high, the signal 1N33 goes low, the signal IN34 remainshigh, and the signal IN35 goes high, so that the transistor 316 isturned on, the transistor 317 is turned on, the transistor 318 is turnedon, and the transistor 319 remains off. Consequently, electricalcontinuity between the node D and the wiring 36 is established. Then,the potential of the wiring 36 (the voltage VDD1) is supplied to thenode D, and thus the potential of the node D increases. Consequently,the transistor 314 is turned on. At that time, the transistor 315remains off, so that electrical continuity between the node C and thewiring 37 is established. Then, the potential of the wiring 37 (thevoltage VSS) is supplied to the node C, and thus the potential of thenode C becomes approximately VSS. Consequently, the transistor 311 isturned off. At that time, the transistor 312 and the transistor 313 areturned on, so that electrical continuity between the wiring 32 and thewiring 33 and electrical continuity between the wiring 32 and the wiring37 are established. Then, the potential of the wiring 37 (the voltageVSS) is supplied to the wiring 32, and thus the potential of the wiring32 becomes approximately VSS. Thus, the signal SOUTi goes low.

Next, in the period T9, the signal 1N34 goes low, which is differentfrom in period T8. Consequently, the transistor 318 is turned off.

The above is the description of an example of the circuit 300. Note thatthe gate of the transistor 317 can be connected to the wiring 34, andthe gate of the transistor 318 can be connected to the wiring 35.

Note that the transistor 319 can be omitted.

Note that the transistor 312 can be omitted.

Embodiment 3

In this embodiment, examples of a display device and an example of apixel included in the display device will be described. In particular,examples of a liquid crystal display device and an example of a pixelincluded in the liquid crystal display device will be described. Adriver circuit of the display device in this embodiment can include thesemiconductor device described in any of Embodiments 1 and 2.

First, an example of the display device in this embodiment will bedescribed.

FIG. 17A shows an example of the display device in this embodiment. Adisplay device in FIG. 17A includes a circuit 1001, a circuit 1002, acircuit 1003_1, a pixel portion 1004, and a terminal 1005. A pluralityof wirings is drawn from the circuit 1003_1 and provided in the pixelportion 1004. The plurality of wirings serves as gate signal lines (alsoreferred to as scan lines). Alternatively, a plurality of wirings isdrawn from the circuit 1002 and provided in the pixel portion 1004. Theplurality of wirings serves as video signal lines (also referred to asdata lines). A plurality of pixels is provided in accordance with theplurality of wirings that is drawn from the circuit 1003_1 and theplurality of wirings that is drawn from the circuit 1002. However, anexample of this embodiment is not limited to this. For example, thepixel portion 1004 can be provided with various other wirings. Thewirings can serve as gate signal lines, data lines, power supply lines,capacity lines, or the like.

In the display device in FIG. 17A, the circuit 1003_1 is formed over asubstrate 1006 over which the pixel portion 1004 is formed, and thecircuit 1001 and the circuit 1002 are formed over a substrate differentfrom the substrate over which the pixel portion 1004 is formed. Thedrive frequency of the circuit 1003_1 is often lower than that of thecircuit 1001 or the circuit 1002. This facilitates the use of anon-single-crystal semiconductor, an amorphous semiconductor, amicrocrystalline semiconductor, an oxide semiconductor, an organicsemiconductor, or the like for a semiconductor layer of a transistor.Thus, the display device can be made larger. Alternatively, the displaydevice can be manufactured at a low cost.

The circuit 1001 has a function of controlling the timing of supplying asignal, voltage, current, or the like to the circuit 1002 and thecircuit 1003_1. Alternatively, the circuit 1001 has a function ofcontrolling the circuit 1002 and the circuit 1003_1. Accordingly, thecircuit 1001 serves as a controller, a control circuit, a timinggenerator, a power supply circuit, a regulator, or the like.

The circuit 1002 has a function of controlling the timing of supplying avideo signal to the pixel portion 1004. Alternatively, the circuit 1002has a function of controlling the luminance or the transmittance of apixel included in the pixel portion 1004. Accordingly, the circuit 1002serves as a driver circuit, a source driver circuit, or a signal linedriver circuit.

The circuit 1003_1 has a function of controlling the timing of supplyinga gate signal to the pixel portion 1004. Alternatively, the circuit1003_1 has a function of controlling the timing of selecting a pixel.Accordingly, the circuit 1003_1 serves as a gate driver (also referredto as a scan line driver circuit).

Note that the display device in this embodiment can include a circuit1003_2 as shown in FIG. 17B. The circuit 1003_2 has a function similarto that of the circuit 1003_1. Further, the circuit 1003_1 and thecircuit 1003_2 drive common wirings, leading to the reduction in load onthe circuit 1003_1 and the circuit 1003_2. However, an example of thisembodiment is not limited to this. For example, the circuit 1003_1 candrive odd-numbered gate signal lines and the circuit 1003_2 can driveeven-numbered gate signal lines. This can lower the drive frequency ofthe circuit 1003_1 and the circuit 1003_2. For another example, thedisplay device in this embodiment can include three or more circuitswhich have a function similar to that of the circuit 1003_1.

Note that in the display device in FIG. 17B, the circuit 1003_1 and thecircuit 1003_2 are formed over the substrate 1006 over which the pixelportion 1004 is formed, and the circuit 1001 and the circuit 1002 areformed over the substrate different from the substrate over which thepixel portion 1004 is formed. The drive frequency of the circuit 1003_1and the circuit 1003_2 is often lower than that of the circuit 1001 orthe circuit 1002. This facilitates the use of a non-single-crystalsemiconductor, an amorphous semiconductor, a microcrystallinesemiconductor, an oxide semiconductor, an organic semiconductor, or thelike for a semiconductor layer of a transistor. Thus, the display devicecan be made larger. Alternatively, the display device can bemanufactured at a low cost.

Note that the circuit 1002, the circuit 1003_1, and the circuit 1003_2can be formed over the substrate 1006 over which the pixel portion 1004is formed, and the circuit 1001 can be formed over a substrate differentfrom the substrate over which the pixel portion 1004 is formed. Thisreduces the number of external circuits, achieving the improvement inreliability, the reduction in manufacturing cost, or the improvement inyield.

Note that a circuit 1002 a which is a part of the circuit 1002, thecircuit 1003_1, and the circuit 1003_2 can be formed over the substrate1006 over which the pixel portion 1004 is formed, and a circuit 1002 bwhich is another part of the circuit 1002 can be provided over asubstrate different from the substrate over which the pixel portion 1004is formed as shown in FIG. 17D. A circuit whose drive frequency iscomparatively low such as a switch, a shift register, and/or a selectorcan be used as the circuit 1002 a. This facilitates the use of anon-single-crystal semiconductor, an amorphous semiconductor, amicrocrystalline semiconductor, an oxide semiconductor, an organicsemiconductor, or the like for a semiconductor layer of a transistor.Thus, the display device can be made larger. Alternatively, the displaydevice can be manufactured at a low cost.

Note that the semiconductor device in any of Embodiments 1 and 2 can beused as a part of the circuit 1003_1, the circuit 1003_2, the circuit1002, and/or the circuit 1002 a. This decreases the drive voltage,thereby leading to the reduction in the power consumption.

Next, an example of the pixel included in the pixel portion 1004 will bedescribed.

FIG. 17E shows an example of the pixel. A pixel 3020 includes atransistor 3021, a liquid crystal element 3022, and a capacitor 3023. Afirst terminal of the transistor 3021 is connected to a wiring 3031. Asecond terminal of the transistor 3021 is connected to one electrode ofthe liquid crystal element 3022 and one electrode of the capacitor 3023.A gate of the transistor 3021 is connected to a wiring 3032. The otherelectrode of the liquid crystal element 3022 is connected to anelectrode 3034. The other electrode of the capacitor 3023 is connectedto a wiring 3033.

A video signal is input from the circuit 1002, which is shown in FIGS.17A to 17D, to the wiring 3031. Consequently, the wiring 3031 serves asa video signal line (also referred to as a source signal line). A gatesignal is input from the circuit 1003_1 and/or the circuit 1003_2, whichare shown in FIGS. 17A to 17D, to the wiring 3032. Therefore, the wiring3032 serves as a gate signal line. The wiring 3033 and the electrode3034 are supplied with a constant voltage from the circuit 1001 shown inFIGS. 17A to 17D. Therefore, the wiring 3033 serves as a power supplyline or a capacity line. Alternatively, the electrode 3034 serves as acommon electrode or a counter electrode. However, an example of thisembodiment is not limited to this. For example, the wiring 3031 can besupplied with a precharge voltage. The precharge voltage hasapproximately the same value as the voltage supplied to the electrode3034 in many cases. For another example, the wiring 3033 can be suppliedwith a signal. Accordingly, a voltage applied to the liquid crystalelement 3022 can be controlled, so that the amplitude of a video signalcan be made small or inversion drive can be realized. For anotherexample, the electrode 3034 can be supplied with a signal. Therefore,frame inversion drive can be realized.

The transistor 3021 has a function of controlling electrical continuitybetween the wiring 3031 and the one electrode of the liquid crystalelement 3022. Alternatively, the transistor 3021 has a function ofcontrolling the timing of when a video signal is written to a pixel.Accordingly, the transistor 3021 serves as a switch. The capacitor 3023has a function of holding a potential difference between the potentialof the one electrode of the liquid crystal element 3022 and thepotential of the wiring 3033. Alternatively, the capacitor 3023 has afunction of holding a voltage applied to the liquid crystal element 3022constant. Thus, the capacitor serves as a storage capacitor.

Embodiment 4

In this embodiment, an example of a semiconductor device and an exampleof the operation of the semiconductor device will be described. Inparticular, an example of a signal line driver circuit and an example ofthe operation of the signal line driver circuit will be described.

First, an example of a signal line driver circuit in this embodimentwill be described.

FIG. 18A shows an example of the signal line driver circuit in thisembodiment. The signal line driver circuit in FIG. 18A includes acircuit 2001 and a circuit 2002. The circuit 2002 includes a pluralityof circuits 2002_1 to 2002_N (N is a natural number). The circuits2002_1 to 2002_N each include a plurality of transistors 2003_1 to 2003_(—) k (k is a natural number). The connection relation in the signalline driver circuit in this embodiment will be described taking thecircuit 2002_1 as an example. First terminals of the transistors 2003_1to 2003 _(—) k are connected to wirings 2004_1 to 2004 _(—) k,respectively. The second terminals of the transistors 2003_1 to 2003_(—) k are connected to wirings S1 to Sk, respectively. The gates of thetransistors 2003_1 to 2003 _(—) k are connected to the wiring 2005_1.

Note that the transistors 2003_1 to 2003 _(—) k are n-channeltransistors. However, an example of this embodiment is not limited tothis; for example, all of the transistors 2003_1 to 2003 _(—) k can bep-channel transistors.

The circuit 2001 has a function of controlling the timing ofsequentially outputting high-level signals to wirings 2005_1 to 2005_N.Alternatively, the circuit 2001 has a function of sequentially selectingthe circuits 2002_1 to 2002_N. Thus, the circuit 2001 serves as a shiftregister. However, an example of this embodiment is not limited to this.For example, the circuit 2001 can output high-level signals to thewirings 2005_1 to 2005_N in different orders. Alternatively, thecircuits 2002_1 to 2002_N can be selected in different orders. Thus, thecircuit 2001 can function as a decoder.

The circuit 2002_1 has a function of controlling the timing of whenelectrical continuity between the wirings 2004_1 to 2004 _(—) k and thewirings S1 to Sk is established. Alternatively, the circuit 2001_1 has afunction of supplying the potentials of the wirings 2004_1 to 2004 _(—)k to the wirings S1 to Sk. Thus, the circuit 2002_1 can function as aselector. Note that each of the circuits 20022 to 2002_N can have afunction that is similar to the function of the circuit 2002_1.

Note that each of the circuits 2002_2 to 2002_N has a similar functionto that of the circuit 2002_1.

Each of the transistors 2003_1 to 2003_N has a function of controllingthe timing of when electrical continuity between the wirings 2004_1 to2004 _(—) k and the wirings S1 to Sk is established. Alternatively, eachof the transistors 2003_1 to 2003_N has a function of controlling thetiming of supplying the potentials of the wirings 2004_1 to 2004 _(—) kto the wirings S1 to Sk. For example, the transistor 2003_1 has afunction of controlling the timing of when electrical continuity betweenthe wiring 2004_1 and the wiring S1 is established. Alternatively, thetransistor 2003_1 has a function of controlling the timing of supplyingthe potentials of the wiring 2004_1 to the wiring S1. Thus, each of thetransistors 2003_1 to 2003_N can function as a switch.

Note that different signals are supplied to the wirings 2004_1 to 2004_(—) k in many cases. The signals are analog signals, in particular,corresponding to image data (also referred to as image signals) in manycases. Thus, the signals can function as video signals. Accordingly, thewirings 2004_1 to 2004 _(—) k can function as signal lines. However, anexample of this embodiment is not limited to this. For example, thesignals can be digital signals, analog voltage, or analog current insome pixel structures.

Next, an example of the operation of the signal line driver circuit inFIG. 18A will be described.

FIG. 18B shows an example of the timing chart which can be used for thesignal line driver circuit in this embodiment. The timing chart in FIG.18B shows examples of signals 2015_1 to 2015_N and signals 2014_1 to2014 _(—) k. The signals 2015_1 to 2015_N are examples of output signalsin the circuit 2001. The signals 2014_1 to 2014 _(—) k are examples ofsignals that are input to the wirings 2004_1 to 2004 _(—) k. Note thatone operation period of the signal line driver circuit corresponds toone gate selection period of the display device. One gate selectionperiod is divided into a period T0 and T1 to TN. The period TO is aperiod for concurrently applying precharge voltage to pixels in aselected row and serves as a precharge period. Each of the periods T1 toTN is a period during which video signals are written to the pixels inthe selected row and serves as a write period.

First, during the period TO, the circuit 2001 supplies high-levelsignals to the wirings 2005_1 to 2005_N. Then, in the circuit 2002_1,for example, the transistors 2003_1 to 2003 _(—) k are turned on so thatelectrical continuity between the wirings 2004_1 to 2004 _(—) k and thewirings S1 to Sk is established. In this case, precharge voltage Vp issupplied to the wirings 2004_1 to 2004 _(—) k. Thus, the prechargevoltage Vp is output to the wirings S1 to Sk through the transistors2003_1 to 2003 _(—) k. Accordingly, the precharge voltage Vp is writtento the pixels in the selected row, so that the pixels in the selectedrow are precharged.

During the periods T1 to TN, the circuit 2001 sequentially outputshigh-level signals to the wirings 2005_1 to 2005_N. For example, duringthe period T1, the circuit 2001 outputs a high-level signal to thewirings 2005_1. Then, the transistors 2003_1 to 2003 _(—) k are turnedon, so that electrical continuity between the wirings 2004_1 to 2004_(—) k and the wirings S1 to Sk is established. In this case, Data (S1)to Data (Sk) are input to the wirings 2004_1 to 2004 _(—) k,respectively. The Data (S1) to Data (Sk) are input to pixels that are ina selected row and in a first to k-th columns through the transistors2003_1 to 2003 _(—) k, respectively. Thus, during the periods T1 to TN,video signals are sequentially written to the pixels in the selected rowby k columns.

As described above, video signals are input to pixels of a plurality ofcolumns at a time, and thus the number of video signals or the number ofwirings can be reduced. Therefore, the number of connections to anexternal circuit can be reduced, achieving the improvement in yield, theimprovement in reliability, the reduction in the number of components,and/or the reduction in cost. Alternatively, video signals are input topixels of a plurality of columns at a time, and thus write time can beextended. This prevents the video signals from being inadequatelywritten to the pixels, so that visual quality can be improved.

Note that the increase in k can decrease the number of connections tothe external circuit. However, if k is too large, the time to inputsignals to pixels is shortened. Therefore, it is preferable that k≦6. Itis more preferable that k≦3. It is much more preferable that k=2.However, an example of this embodiment is not limited to this.

In particular, in the case where the number of color elements of a pixelis n (n is a natural number), it is preferable that k=n or k=n×d (d is anatural number). For example, in the case where the color element of thepixel is divided into three colors: red (R), green (G), and blue (B), itis preferable that k=3 or k=3×d. However, an example of this embodimentis not limited to this. For example, in the case where the pixel isdivided into m (m is a natural number) pieces of sub-pixels, k=m ork=m×d is preferable. For example, in the case where the pixel is dividedinto two sub-pixels, k=2 is preferable. Alternatively, in the case wherethe number of color elements of the pixel is n, it is preferable thatk=m×n or k=m×n×d. However, an example of this embodiment is not limitedto this.

Note that all of the signal line driver circuits in this embodiment canbe formed over the substrate over which the pixel portion is formed, andall of the signal line driver circuits in this embodiment can be formedover a substrate (e.g., a silicon substrate or SOI substrate) differentfrom the substrate over which the pixel portion is formed.Alternatively, a part of the signal line driver circuits in thisembodiment (e.g., the circuit 2002) can be formed over the substrateover which the pixel portion is formed, and another part of the signalline driver circuits in this embodiment (e.g., the circuit 2001) can beformed over a substrate different from the substrate over which thepixel portion is formed.

FIG. 18C shows an example of the structure in which the circuit 2001 andthe circuit 2002 are formed over the substrate over which the pixelportion 2007 is formed. In this structure, the number of connectionsbetween the substrate over which the pixel portion is formed and anexternal circuit can be reduced, achieving the improvement in yield, theimprovement in reliability, the reduction in the number of components,or the reduction in cost. In particular, by also forming a scan linedriver circuit 2006A and a scan line driver circuit 2006B over thesubstrate over which the pixel portion 2007 is formed, the number ofconnections to the external circuit can be further reduced.

FIG. 18D shows an example of the structure in which the circuit 2002 isformed over the substrate over which the pixel portion 2007 is formed,and the circuit 2001 is formed over a substrate different from thesubstrate over which the pixel portion 2007 is formed. In this casealso, the number of connections between the substrate over which thepixel portion is formed and the external circuit can be reduced,achieving the improvement in yield, the improvement in reliability, thereduction in the number of components, or the reduction in cost.Alternatively, the number of circuits which are formed over thesubstrate over which the pixel portion 2007 is formed is reduced, andthus the size of a frame can be reduced.

Note that the semiconductor device in Embodiments 1 and 2 can be usedfor the circuit 2001. Consequently, the drive voltage can be decreasedand thus, the power consumption can be reduced. Alternatively, since allof the transistors can be n-channel transistors, the number of steps canbe reduced. Thus, the improvement in yield, the reduction inmanufacturing cost, and the improvement in reliability can be achieved.

Embodiment 5

In this embodiment, an example of the structure of a semiconductordevice will be described. The structure of a transistor, in particular,will be described.

First, the structure of a transistor in this embodiment will bedescribed.

FIG. 19A shows an example of a top-gate transistor and an example of adisplay element formed over the top-gate transistor. A transistor inFIG. 19A includes a substrate 5260; an insulating layer 5261; asemiconductor layer 5262 including a region 5262 a, a region 5262 b, aregion 5262 c, a region 5262 d, and a region 5262 e; an insulating layer5263; a conductive layer 5264; an insulating layer 5265 includingopenings; and a conductive layer 5266. The insulating layer 5261 isformed over the substrate 5260. The semiconductor layer 5262 is formedover the insulating layer 5261. The insulating layer 5263 is formed soas to cover the semiconductor layer 5262. The conductive layer 5264 isformed over the semiconductor layer 5262 and the insulating layer 5263.The insulating layer 5265 is formed over the insulating layer 5263 andthe conductive layer 5264. The conductive layer 5266 is formed over theinsulating layer 5265 and in the openings formed in the insulating layer5265. Thus, the top-gate transistor is formed.

FIG. 19B shows an example of a bottom-gate transistor and an example ofa display element formed over the bottom-gate transistor. A transistorin FIG. 19B includes a substrate 5300, a conductive layer 5301, aninsulating layer 5302, a semiconductor layer 5303 a, a semiconductorlayer 5303 b, a conductive layer 5304, an insulating layer 5305including an opening, and a conductive layer 5306. The conductive layer5301 is formed over the substrate 5300. The insulating layer 5302 isformed so as to cover the conductive layer 5301. The semiconductor layer5303 a is formed over the conductive layer 5301 and the insulating layer5302. The semiconductor layer 5303 b is formed over the semiconductorlayer 5303 a. The conductive layer 5304 is formed over the semiconductorlayer 5303 b and the insulating layer 5302. The insulating layer 5305 isformed over the insulating layer 5302 and the conductive layer 5304. Theconductive layer 5306 is formed over the insulating layer 5305 and inthe opening formed in the insulating layer 5305. Thus, the bottom-gatetransistor is formed.

FIG. 19C shows an example of a transistor formed over a semiconductorsubstrate. A transistor in FIG. 19C includes a semiconductor substrate5352 including a region 5353 and a region 5355; an insulating layer5356; an insulating layer 5354; a conductive layer 5357; an insulatinglayer 5358 including openings; and a conductive layer 5359. Theinsulating layer 5356 is formed over the semiconductor substrate 5352.The insulating layer 5354 is formed over the semiconductor substrate5352. The conductive layer 5357 is formed over the insulating layer5356. The insulating layer 5358 is formed over the insulating layer5354, the insulating layer 5356, and the conductive layer 5357. Theconductive layer 5359 is formed over the insulating layer 5358 and inthe openings formed in the insulating layer 5358. Thus, the transistoris formed in each of a region 5350 and a region 5351.

Note that in the case of any of the transistors in FIGS. 19A to 19C, aninsulating layer 5267 including an opening, a conductive layer 5268, aninsulating layer 5269 including an opening, a light-emitting layer 5270,and a conductive layer 5271 can be formed over the transistor, as shownin FIG. 19A. The insulating layer 5267 is formed over the conductivelayer 5266 and the insulating layer 5265. The conductive layer 5268 isformed over the insulating layer 5267 and in the opening formed in theinsulating layer 5267. The insulating layer 5269 is formed over theinsulating layer 5267 and the conductive layer 5268. The light-emittinglayer 5270 is formed over the insulating layer 5269 and in the openingformed in the insulating layer 5269. The conductive layer 5271 is formedover the insulating layer 5269 and the light-emitting layer 5270.

Note that in the case of any of the transistors in FIGS. 19A to 19C, aliquid crystal layer 5307 and a conductive layer 5308 can be formed overthe transistor as shown in FIG. 19B. The liquid crystal layer 5307 isformed over the insulating layer 5305 and the conductive layer 5306. Theconductive layer 5308 is formed over the liquid crystal layer 5307.

Note that various components other than the layers in FIG. 19A to 19Ccan be formed. For example, an insulating layer which serves as analignment film and/or an insulating layer which serves as a protrudingportion can be formed over the insulating layer 5305 and the conductivelayer 5306. For another example, an insulating layer which serves as aprojection, a color filter, and/or a black matrix can be formed over theconductive layer 5308. For another example, an insulating layer whichserves as an alignment film can be formed below the conductive layer5308.

Note that each of the region 5262 c and the region 5262 e is a region towhich an impurity is added and serves as a source region or a drainregion. Each of the region 5262 b and the region 5262 d is a region towhich a lower concentration of an impurity than that added to the region5262 c or the region 5262 e and serves as an LDD (lightly doped drain)region. The region 5262 a is a region to which an impurity is not addedand serves as a channel region. However, one example of this embodimentis not limited to this. For example, an impurity can be added to theregion 5262 a. Thus, it is possible to improve the characteristics ofthe transistor and control the threshold voltage. However, theconcentration of the impurity added to the region 5262 a is preferablylower than the concentration of an impurity added to the region 5262 b,the region 5262 c, the region 5262 d, or the region 5262 e. For anotherexample, the region 5262 c or the region 5262 e can be omitted.Alternatively, only an n-channel transistor can be provided with theregion 5262 c or the region 5262 e.

Note that the semiconductor layer 5303 b is a semiconductor layer towhich phosphorus or the like is added as an impurity element and hasn-type conductivity. Note that when an oxide semiconductor or a compoundsemiconductor is used for the semiconductor layer 5303 a, thesemiconductor layer 5303 b can be omitted.

Note that a single crystal silicon substrate having n-type or p-typeconductivity, for example, can be used as a semiconductor substrate(e.g., the semiconductor substrate 5352). In addition, the region 5353is a region, to which an impurity has been added, in the semiconductorsubstrate 5352 and serves as a well. For example, when the semiconductorsubstrate 5352 has p-type conductivity, the region 5353 has n-typeconductivity. On the other hand, for example, when the semiconductorsubstrate 5352 has n-type conductivity, the region 5353 has p-typeconductivity. The region 5355 is a region in the semiconductor substrate5352, to which region an impurity has been added, and serves as a sourceregion or a drain region. Note that an LDD region can be formed in thesemiconductor substrate 5352.

Next, an example of the function of each layer will be described.

The insulating layer 5261 serves as a foundation film. The insulatinglayer 5354 serves as a device isolation layer (e.g., a field oxide).Each of the insulating layer 5263, the insulating layer 5302, and theinsulating layer 5356 serves as a gate insulating film. Each of theconductive layer 5264, the conductive layer 5301, and the conductivelayer 5357 can serve as a gate electrode. Each of the insulating layer5265, the insulating layer 5267, the insulating layer 5305, and theinsulating layer 5358 serves as an interlayer or a planarizing film.Each of the conductive layer 5266, the conductive layer 5304, and theconductive layer 5359 serves as a wiring, an electrode of a transistor,an electrode of a capacitor, or the like. Each of the conductive layer5268 and the conductive layer 5306 serves as a pixel electrode, areflective electrode, or the like. The insulating layer 5269 serves as apartition. Each of the conductive layer 5271 and the conductive layer5308 serves as a counter electrode, a common electrode, or the like.However, one example of this embodiment is not limited to this.

Next, the material, structure, characteristics of each layer and thelike will be described.

Examples of the substrate (e.g., the substrate 5260 or the substrate5300) include a semiconductor substrate (e.g., a single crystalsubstrate or a silicon substrate), an SOI substrate, a glass substrate,a quartz substrate, a plastic substrate, a metal substrate, a stainlesssteel substrate, a substrate containing stainless steel foil, a tungstensubstrate, a substrate containing tungsten foil, a flexible substrate, abonding film, paper containing a fibrous material, and a base film.Examples of the material for the glass substrate include a bariumborosilicate glass, an aluminoborosilicate, and soda lime. Examples ofthe material for the flexible substrate include a flexible syntheticresin such as plastics typified by polyethylene terephthalate (PET),polyethylene naphthalate (PEN), and polyether sulfone (PES), and aflexible synthetic resin such as acrylic. Examples of the material forthe bonding film include polypropylene, polyester, vinyl, polyvinylfluoride, and polyvinyl chloride. Examples of the material for the basefilm include polyester, polyamide, polyimide, inorganic vapor depositionfilm, and paper. Specifically, the use of semiconductor substrates,single crystal substrates, SOI substrates, or the like enables themanufacture of small-sized transistors with a small variation incharacteristics, size, shape, or the like and with high currentcapability. A circuit using such transistors achieves lower powerconsumption of the circuit or higher integration of the circuit.

Note that it is possible to form a transistor over a substrate and thentranspose the transistor to another substrate. Examples of the anothersubstrate include, in addition to the above-described substrates, apaper substrate, a cellophane substrate, a stone substrate, a woodsubstrate, a cloth substrate (a natural fiber (e.g., silk, cotton, orhemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), aregenerated fiber (e.g., acetate, cupra, rayon, or regeneratedpolyester), or the like), a leather substrate, and a rubber substrate.The use of these substrates provides transistors with excellentproperties, transistors which consume low power, devices with highdurability, high heat resistance, light weight, or small thickness.

Note that all the circuits needed to realize a predetermined functioncan be formed over the same substrate (e.g., a glass substrate, aplastic substrate, a single crystal substrate, or an SOI substrate).This achieves cost reduction by the reduced number of components or theimprovement in reliability by the reduced number of connection points tocircuit components.

Note that it is possible to form not all the circuits needed to realizethe predetermined function over the same substrate. That is, a part ofthe circuits needed to realize the predetermined function can be formedover a substrate and another part of the circuits needed to realize thepredetermined function can be formed over another substrate. Forexample, a part of the circuits needed to realize the predeterminedfunction can be formed over a glass substrate and a part of the circuitsneeded to realize the predetermined function can be formed over a singlecrystal substrate (or an SOI substrate). Then, a single crystalsubstrate over which a part of the circuits needed to realize thepredetermined function (such a substrate is also referred to as an ICchip) can be connected to a glass substrate by COG (chip on glass), andan IC chip can be provided over the glass substrate. Alternatively, anIC chip can be connected to a glass substrate using TAB (tape automatedbonding), COF (chip on film), SMT (surface mount technology), a printedcircuit board, or the like.

For example, the insulating layers (e.g., the insulating layer 5261, theinsulating layer 5263, the insulating layer 5265, the insulating layer5267, the insulating layer 5269, the insulating layer 5305, theinsulating layer 5356, and the insulating layer 5358) each have asingle-layer or multilayer structure of a film containing oxygen ornitrogen (e.g., silicon oxide (SiOx), silicon nitride (SiNx), siliconoxynitride (SiOxNy) (x>y>0), and silicon nitride oxide (SiNxOy)(x>y>0)), a film containing carbon (e.g., DLC (diamond-like carbon)), anorganic material (e.g., siloxane resin, an epoxy, polyimide, polyamide,polyvinylphenol, benzocyclobutene, acrylic, or the like), or the like.However, one example of this embodiment is not limited to this.

Note that when the insulating layer has a two-layer structure, a siliconnitride film and a silicon oxide film are provided as a first insulatinglayer and a second insulating layer, respectively. When the insulatinglayer has a three-layer structure, a silicon oxide film, a siliconnitride film, and a silicon oxide film are provided as a firstinsulating layer, a second insulating layer, and a third insulatinglayer, respectively.

Examples of the material of the semiconductor layers (e.g., thesemiconductor layer 5262, the semiconductor layer 5303 a, and thesemiconductor layer 5303 b) include a non-single-crystal semiconductor(e.g., amorphous silicon, polycrystalline silicon, or microcrystallinesilicon), a single crystal semiconductor, a compound semiconductor or anoxide semiconductor (e.g., ZnO, InGaZnO, SiGe, GaAs, IZO (indium zincoxide), ITO (indium tin oxide), SnO, TiO, or AlZnSnO (AZTO)), an organicsemiconductor, and a carbon nanotube.

Note that using a catalyst (e.g., nickel) when manufacturingpolycrystalline silicon or microcrystalline silicon further improvescrystallinity and enables the manufacture of thin film transistorshaving excellent electric characteristics. It is thus possible to form agate driver circuit (e.g., a scan line driver circuit), a source drivercircuit (e.g., a signal line driver circuit), a part of the sourcedriver circuit (e.g., a switch for dividing a video signal), a signalprocessing circuit (e.g., a signal generating circuit, a gammacorrection circuit, or a DA converter circuit), or the like, over thesame substrate. When microcrystalline silicon is manufactured by acatalyst (e.g., nickel), in particular, it is possible to improvecrystallinity by only heat treatment without laser irradiation.Therefore, variations in the crystallinity of silicon can be reduced,leading to display of images with improved image quality. Note that itis possible to manufacture polycrystalline silicon or microcrystallinesilicon without a catalyst (e.g., nickel).

Note that although preferably, crystallinity of silicon is improved topolycrystal, microcrystal, or the like in the whole panel, the presentinvention is not limited to this. It is acceptable that thecrystallinity of silicon is improved only in part of the panel.Selective improvement in crystallinity can be achieved by selectivelaser irradiation or the like. For example, only the region of a circuitthat needs to operate at high speed, such as the region of a peripheralcircuit other than pixels, the region of a gate driver circuit and asource driver circuit, a part of the source driver circuit (e.g., ananalog switch), and the like can be irradiated with laser beam. On theother hand, the need for a pixel region to operate at high speed is notconsiderable, and a pixel circuit can thus operate without any problemseven if the crystallinity is not improved. This makes the region smallwhose crystallinity should be improved, thereby shortening themanufacturing process. Thus, throughput can be increased andmanufacturing cost can be reduced. Alternatively, the manufacture needsthe small number of manufacturing apparatuses, so that manufacturingcost can be reduced.

For example, each of the conductive layers (e.g., the conductive layer5264, the conductive layer 5266, the conductive layer 5268, theconductive layer 5271, the conductive layer 5301, the conductive layer5304, the conductive layer 5306, the conductive layer 5308, theconductive layer 5357, and the conductive layer 5359) is a single-layerfilm or a multilayer film. Examples of the material for the single-layerfilm include the group consisting of aluminum (Al), tantalum (Ta),titanium (Ti), molybdenum (Mo), tungsten (W), neodymium (Nd), chromium(Cr), nickel (Ni), platinum (Pt), gold (Au), silver (Ag), copper (Cu),manganese (Mn), cobalt (Co), niobium (Nb), silicon (Si), iron (Fe),palladium (Pd), carbon (C), scandium (Sc), zinc (Zn), gallium (Ga),indium (In), tin (Sn), zirconium (Zr), and cerium (Ce); an elementselected from the above group; and a compound containing one or moreelements selected from the above group. Other examples of the materialfor the single-layer film include a nanotube material (e.g., a carbonnanotube, an organic nanotube, an inorganic nanotube, or a metalnanotube), a film containing a polymeric material, and conductiveplastic (e.g., polyethylene dioxythiophene (PEDOT)). Note that thesignel-layer film can contain phosphorus (P), boron (B), arsenic (As),and/or oxygen (O).

Note that examples of the compound include a compound containing one ormore elements selected from the above group (e.g., an alloy), a compoundof nitrogen with one or more of elements selected from the above group(e.g., a nitride film), and a compound of silicon with one or more ofelements selected from the above group (e.g., a silicide film). Examplesof the alloy include indium tin oxide (ITO), indium zinc oxide (IZO),indium tin oxide containing silicon oxide (ITSO), zinc oxide (ZnO), tinoxide (SnO), cadmium tin oxide (CTO), aluminum-neodymium (Al—Nd),aluminum-tungsten (Al—W), aluminum-zirconium (Al—Zr), aluminum titanium(Al—Ti), aluminum-cerium (Al—Ce), magnesium-silver (Mg—Ag),molybdenum-niobium (Mo—Nb), molybdenum-tungsten (Mo—W), andmolybdenum-tantalum (Mo—Ta). Examples of the nitride film includetitanium nitride, tantalum nitride, and molybdenum nitride. Examples ofthe silicide film include tungsten silicide, titanium silicide, nickelsilicide, aluminum silicon, and molybdenum silicon.

Examples of the light-emitting layer (e.g., the light-emitting layer5270) include an organic EL element, and an inorganic EL element.Examples of the organic EL element include a single-layer or multilayerstructure of a hole injection layer using a hole injection material, ahole transport layer using a hole transport material, a light-emittinglayer using a light-emitting material, an electron transport layer usingan electron transport material, an electron injection layer using anelectron injection material, and a layer formed by mixing a plurality ofmaterials selected from these materials.

An example of the liquid crystal layer 5307 is an element which controlstransmission or non-transmission of light by optical modulation actionof liquid crystals. The element can be formed using a pair of electrodesand a liquid crystal layer. Note that the optical modulation action ofliquid crystals is controlled by an electric filed applied to the liquidcrystal (including a lateral electric field, a vertical electric fieldand a diagonal electric field). Specifically, examples of the liquidcrystal element include a nematic liquid crystal, a cholesteric liquidcrystal, a smectic liquid crystal, a discotic liquid crystal, athermotropic liquid crystal, a lyotropic liquid crystal, a low molecularliquid crystal, a high molecular liquid crystal, a PDLC (polymerdispersed liquid crystal), a ferroelectric liquid crystal, ananti-ferroelectric liquid crystal, a main chain type liquid crystal, aside chain type polymer liquid crystal, a plasma addressed liquidcrystal (PALC), a banana-shaped liquid crystal, a TN (twisted nematic)mode, an STN (super twisted nematic) mode, an IPS (in-plane-switching)mode, an FFS (fringe field switching) mode, an MVA (multi-domainvertical alignment) mode, a PVA (patterned vertical alignment) mode, anASV (advanced super view) mode, an ASM (axially symmetric alignedmicrocell) mode, an OCB (optical compensated birefringence) mode, an ECB(electrically controlled birefringence) mode, an FLC (ferroelectricliquid crystal) mode, an AFLC (anti-ferroelectric liquid crystal) mode,a PDLC (polymer dispersed liquid crystal) mode, a PNLC (polymer networkliquid crystal) mode, a guest-host mode, and a blue-phase mode.

Note that each layer included in the above transistor can be formedusing an inkjet method or a printing method. Thus, the transistor can bemanufactured at room temperature, manufactured in a low vacuum, ormanufactured to be over a large substrate. The transistor thus can bemanufactured without a mask (reticle), a layout of the transistor can bechanged easily. Alternatively, since the transistor can be formedwithout use of a resist, material cost is reduced and the number ofsteps can be reduced.

Further, since a film can be formed where needed, a material is notwasted as compared to a manufacturing method by which etching isperformed after the film is formed over the entire surface, so that costcan be reduced.

The above is the description of one example of the structure of thetransistor in this embodiment. However, the structure of the transistoris not limited to the above structure; the transistor can have variousother structures.

For example, a MOS transistor, a junction transistor, a bipolartransistor, or the like can be used as the transistor. By using a MOStransistor, in particular, the size of the transistor can be reduced. Byusing a bipolar transistor, in particular, a large amount of current canflow. Thus, a circuit can be operated at high speed.

For another example, the transistor can have gate electrodes above andbelow a channel. A structure where the gate electrodes are providedabove and below the channel gives a circuit structure where a pluralityof transistors are connected in parallel. As a result, a channel regionis increased, thereby increasing the current value. Alternatively,because a structure where the gate electrodes are provided above andbelow the channel causes a depletion layer to easily occur, asubthreshold swing (an S value) can be reduced.

For another example, the transistor can have the structure where a gateelectrode is provided above a channel region, the structure where a gateelectrode is provided below a channel region, a staggered structure, aninverted staggered structure, the structure where a channel region isdivided into a plurality of regions, the structure where channel regionsare connected in parallel or in series, or the like.

For another example, the transistor can have the structure where thesource electrode or the drain electrode overlaps with the channel region(or part thereof). The structure where the source electrode or the drainelectrode overlaps with the channel region (or part thereof) preventsunstable operation due to electric charge accumulated in part of thechannel region.

The transistor in this embodiment can be used for the semiconductordevice or the display device in any of Embodiments 1 to 4.

Embodiment 6

An example of a cross-sectional structure of a display device will bedescribed in this embodiment.

FIG. 20A shows an example of the top view of a display device. A drivercircuit 5392 and a pixel portion 5393 are formed over a substrate 5391.Examples of the driver circuit 5392 include a scan line driver circuit,a signal line driver circuit, and the like.

FIG. 20B shows an example of a section A-B of a display device in FIG.20A. The display device includes a substrate 5400, a conductive layer5401, an insulating layer 5402, a semiconductor layer 5403 a, asemiconductor layer 5403 b, a conductive layer 5404, an insulating layer5405, a conductive layer 5406, an insulating layer 5408, a liquidcrystal layer 5407, a conductive layer 5409, and a substrate 5410. Theconductive layer 5401 is formed over the substrate 5400. The insulatinglayer 5402 is formed so as to cover the conductive layer 5401. Thesemiconductor layer 5403 a is formed over the conductive layer 5401 andthe insulating layer 5402. The semiconductor layer 5403 b is formed overthe semiconductor layer 5403 a. The conductive layer 5404 is formed overthe semiconductor layer 5403 b and the insulating layer 5402. Theinsulating layer 5405 is formed over the insulating layer 5402 and theconductive layer 5404 and has an opening. The conductive layer 5406 isformed over the insulating layer 5405 and in the openings formed in theinsulating layer 5405. The liquid crystal layer 5407 is formed over theinsulating layer 5405. The insulating layer 5408 is formed over theinsulating layer 5405 and the conductive layer 5406. The conductivelayer 5409 is formed over the liquid crystal layer 5407 and theinsulating layer 5405.

The conductive layer 5401 serves as a gate electrode. The insulatinglayer 5402 can serve as a gate insulating film. The conductive layer5404 can serve as a wiring, an electrode of a transistor, an electrodeof a capacitor, or the like. The insulating layer 5405 can serve as aninterlayer or a planarizing film. The conductive layer 5406 can serve asa wiring, a pixel electrode, or a reflecting electrode. The insulatinglayer 5408 can serve as a sealant. The conductive layer 5409 can serveas a counter electrode or a common electrode.

Here, parasitic capacitance can exist between the driver circuit 5392and the conductive layer 5409. Accordingly, an output signal from thedriver circuit 5392 or the potential of each node can be distorted ordelayed. This increases power consumption. However, the insulating layer5408, which can serve as a sealant, formed over the driver circuit 5392as shown in FIG. 20B can reduce parasitic capacitance between the drivercircuit 5392 and the conductive layer 5409. This is because thedielectric constant of the sealant is often lower than the dielectricconstant of the liquid crystal layer. Therefore, distortion or delay ofthe output signal from the driver circuit 5392 or the potential of eachnode can be reduced. This reduces the power consumption.

Note that as shown in FIG. 20C, the insulating layer 5408 which canserve as a sealant can be formed over a part of the driver circuit 5392.Even in such a case also, parasitic capacitance between the drivercircuit 5392 and the conductive layer 5409 can be reduced, and thusdistortion or delay of the output signal from the driver circuit 5392 ordistortion or delay of the potential of each node can be reduced.

Note that a display element is not limited to a liquid crystal element;a variety of display elements such as an EL element and anelectrophoretic element can be used.

Note that the structure of the display device in this embodiment can beapplied to the semiconductor device or display device in Embodiments 1to 5. For example, in the case where a non-single-crystal semiconductor,a microcrystalline semiconductor, an organic semiconductor, an oxidesemiconductor, or the like is used for a semiconductor layer of atransistor, the channel width of the transistor is often large. However,by reducing parasitic capacitance of the driver circuit as in thisembodiment, the channel width of the transistor can be made small. Thisreduces a layout area, so that the frame of the display device can bemade small. Alternatively, the display device can have higherdefinition.

Embodiment 7

In this embodiment, an example of a semiconductor device and an exampleof a manufacturing process of the semiconductor device will bedescribed. In particular, an example of the manufacturing process of atransistor and an example of the manufacturing process of a capacitorwill be described. In particular, a manufacturing process where an oxidesemiconductor is used for a semiconductor layer will be described.

FIGS. 21A to 21C show an example of the manufacturing process of atransistor and a capacitor. A transistor 5441 is an inverted staggeredthin film transistor. In the transistor 5441, a wiring is provided overan oxide semiconductor layer with a source electrode or a drainelectrode therebetween.

First, a first conductive layer is formed over the entire surface of asubstrate 5420 by sputtering. Next, the first conductive layer isselectively etched with the use of a resist mask formed through aphotolithography process using a first photomask, forming a conductivelayer 5421 and a conductive layer 5422. The conductive layer 5421 canserve as a gate electrode. The conductive layer 5422 can serve as one ofelectrodes of the capacitor. Note that an example of this embodiment isnot limited to this; each of the conductive layers 5421 and 5422 caninclude a portion serving as a wiring, a gate electrode, or an electrodeof the capacitor. After that, the resist mask is removed.

Next, an insulating layer 5423 is formed by plasma-enhanced CVD orsputtering. The insulating layer 5423 can serve as a gate insulatinglayer and is formed so as to cover the conductive layers 5421 and 5422.Note that the thickness of the insulating layer 5423 is often 50 to 250nm.

Next, the insulating layer 5423 is selectively etched with the use of aresist mask formed through a photolithography process using a secondphotomask, so that a contact hole 5424 which reaches the conductivelayer 5421 is formed. Then, the resist mask is removed. Note that anexample of this embodiment is not limited to this; the contact hole 5424can be omitted. Alternatively, the contact hole 5424 can be formed afteran oxide semiconductor layer is formed. A cross-sectional view of thesteps so far corresponds to FIG. 21A.

Next, an oxide semiconductor layer is formed over the entire surface bysputtering. Note that an example of this embodiment is not limited tothis; it is possible to form the oxide semiconductor layer by sputteringand to form a buffer layer (e.g., an n⁺ layer) thereover. Note that thethickness of the oxide semiconductor layer is often 5 to 200 nm.

Next, the oxide semiconductor layer is selectively etched using a thirdphotomask. After that, the resist mask is removed.

Next, a second conductive layer is formed over the entire surface bysputtering. Then, the second conductive layer is selectively etched withthe use of a resist mask formed through a photolithography process usinga fourth photomask, so that a conductive layer 5429, a conductive layer5430, and a conductive layer 5431 are formed. The conductive layer 5429is connected to the conductive layer 5421 through the contact hole 5424.The conductive layers 5429 and 5430 can serve as the source electrodeand the drain electrode. The conductive layer 5431 can serve as theother of the electrodes of the capacitor. Note that this embodiment isnot limited to this; each of the conductive layers 5429, 5430, and 5431can include a portion serving as a wiring, the source electrode, thedrain electrode, or the electrode of the capacitor. A cross-sectionalview of the steps so far corresponds to FIG. 21B.

Next, heat treatment is performed at 200 to 600° C. in an air atmosphereor a nitrogen atmosphere. This heat treatment leads to rearrangement ofan In—Ga—Zn—O based non-single-crystal layer at an atomic level. In thismanner, through heat treatment (the heat treatment can be annealing withlight), strain which inhibits carrier movement is released. Note thatthere is no particular limitation on the timing of when the heattreatment is performed, and the heat treatment can be performed atdifferent timings after the oxide semiconductor layer is formed.

Next, an insulating layer 5432 is formed over the entire surface. Theinsulating layer 5432 can be either single-layer or multilayer. Forexample, in the case where an organic insulating layer is used as theinsulating layer 5432, the organic insulating layer is formed in such amanner that a composition which is a material for the organic insulatinglayer is applied and subjected to heat treatment at 200 to 600° C. in anair atmosphere or a nitrogen atmosphere. By forming the organicinsulating layer that is in contact with the oxide semiconductor layerin this manner, a thin film transistor which has high reliability interms of electric characteristics can be made. Note that in the casewhere an organic insulating layer is used as the insulating layer 5432,a silicon nitride film or a silicon oxide film can be provided below theorganic insulating layer.

Next, a third conductive layer is formed over the entire surface. Then,the third conductive layer is selectively etched with the use of aresist mask formed through a photolithography process using a fifthphotomask, so that a conductive layer 5433 and a conductive layer 5434are formed. A cross-sectional view of the steps so far corresponds toFIG. 21C. Each of the conductive layers 5433 and 5434 can serve as awiring, a pixel electrode, a reflecting electrode, a light-transmittingelectrode, or the electrode of the capacitor. In particular, since theconductive layer 5434 is connected to the conductive layer 5422, theconductive layer 5434 can serve as the electrode of the capacitor 5442.Note that an example of this embodiment is not limited to this; theconductive layers 5433 and 5434 can have the function of connecting thefirst conductive layer to the second conductive layer to each other. Forexample, by connecting the conductive layers 5433 and 5434 to eachother, the conductive layer 5422 and the conductive layer 5430 can beconnected to each other with the third conductive layer (the conductivelayers 5433 and 5434) therebetween.

The transistor 5441 and the capacitor 5442 can be manufactured throughthe above steps. The transistor in this embodiment can be used for thesemiconductor device or display device in Embodiments 1 to 8.

Note that as shown in FIG. 21D, an insulating layer 5435 can be formedover the oxide semiconductor layer 5425.

Note that as shown in FIG. 21E, the oxide semiconductor layer 5425 canbe formed after the second conductive layer is patterned.

Note that for the substrate, the insulating film, the conductive film,and the semiconductor layer in this embodiment, the materials describedin the other embodiments or the materials described in thisspecification can be used.

Embodiment 8

In this embodiment, examples of an electronic appliance are described.

FIGS. 22A to 22H and FIGS. 23A to 23D show electronic appliances. Theseelectronic appliances can each include a housing 5000, a display portion5001, a speaker 5003, an LED lamp 5004, operation keys 5005 (including apower switch or an operation switch), a connection terminal 5006, asensor 5007 (a sensor having the function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared ray), a microphone 5008, and the like.

FIG. 22A shows a mobile computer, which can include a switch 5009, aninfrared port 5010, and the like in addition to the above objects. FIG.22B shows a portable image reproducing device provided with a memorymedium (e.g., a DVD reproducing device) that can include a seconddisplay portion 5002, a memory medium reading portion 5011, and the likein addition to the above objects. FIG. 22C shows a goggle-type displaythat can include the second display portion 5002, a support portion5012, an earphone 5013, and the like in addition to the above objects.FIG. 22D shows a portable game machine that can include the memorymedium reading portion 5011 and the like in addition to the aboveobjects. FIG. 22E shows a digital camera with a television receiverfunction which can include an antenna 5014, a shutter button 5015, animage receiving portion 5016, and the like in addition to the aboveobjects. FIG. 22F shows a portable game console that can include thesecond display portion 5002, the memory medium reading portion 5011, andthe like in addition to the above objects. FIG. 22G shows a televisionreceiver that can include a tuner, an image processing portion, and thelike in addition to the above objects. FIG. 22H shows a portabletelevision receiver that can include a charger 5017 capable oftransmitting and receiving signals and the like in addition to the aboveobjects. FIG. 23A shows a display that can include a support 5018 andthe like in addition to the above objects. FIG. 23B shows a camera thatcan include an external connection port 5019, a shutter button 5015, animage receiving portion 5016, and the like in addition to the aboveobjects. FIG. 23C shows a computer that can include a pointing device5020, the external connection port 5019, a reader/writer 5021, and thelike in addition to the above objects. FIG. 23D shows a mobile phonethat can include a transmitter, a receiver, a tuner of one-segment (1segdigital TV broadcasts) partial reception service for mobile phones andmobile terminals, and the like in addition to the above objects.

The electronic appliances shown in FIGS. 22A to 22H and FIGS. 23A to 23Dcan have a variety of functions, for example, the function of displayinga lot of information (e.g., a still image, a moving image, and a textimage) on a display portion; a touch panel function; the function ofdisplaying a calendar, date, time, and the like; the function ofcontrolling processing with a lot of software (programs); a wirelesscommunication function; the function of being connected to a variety ofcomputer networks with a wireless communication function; the functionof transmitting and receiving a lot of data with a wirelesscommunication function; the function of reading a program or data storedin a memory medium and displaying the program or data on a displayportion. Further, the electronic appliance including a plurality ofdisplay portions can have the function of displaying image informationmainly on one display portion while displaying text information onanother display portion, the function of displaying a three-dimensionalimage by displaying images where parallax is considered on a pluralityof display portions, or the like. Furthermore, the electronic applianceincluding an image receiving portion can have the function ofphotographing a still image, the function of photographing a movingimage, the function of automatically or manually correcting aphotographed image, the function of storing a photographed image in amemory medium (an external memory medium or a memory medium incorporatedin the camera), the function of displaying a photographed image on thedisplay portion, or the like. Note that functions that can be providedfor the electronic appliances shown in FIGS. 22A to 22H and FIGS. 23A to23D are not limited them, and the electronic appliances can have avariety of functions.

The electronic appliances in this embodiment each include a displayportion for displaying some kind of information. The use of thesemiconductor device which is described or display device in Embodiments1 to 9 as the display portion reduces manufacturing cost and improvesreliability or yield.

Next, example applications for the semiconductor device will bedescribed.

FIG. 23E shows an example in which a semiconductor device isincorporated in a building structure. FIG. 23E shows a housing 5022, adisplay portion 5023, a remote controller 5024 which is an operatingportion, a speaker 5025, and the like. The semiconductor device isincorporated in the building structure so as to be hung on the wall; thesemiconductor device can be provided without a large space.

FIG. 23F shows another example in which a semiconductor device isincorporated in a building structure. A display panel 5026 isincorporated in a prefabricated bath unit 5027, so that a bather canview the display panel 5026.

Note that although in this embodiment, the wall and the prefabricatedbath are given as examples of the building structure, this embodiment isnot limited to this. The semiconductor devices can be provided in avariety of building structures.

Next, examples in which semiconductor devices are incorporated in movingobjects will be described.

FIG. 23G shows an example in which a semiconductor device isincorporated in a car. A display panel 5028 is incorporated in a carbody 5029 of the car and can display information related to theoperation of the car or information input from inside or outside of thecar on demand. Note that the display panel 5028 can have a navigationfunction.

FIG. 23H shows an example in which a semiconductor device isincorporated in a passenger airplane. FIG. 23H shows a usage patternwhen a display panel 5031 is provided to a ceiling 5030 which is above aseat of the passenger airplane. The display panel 5031 is incorporatedin the ceiling 5030 through a hinge portion 5032, and a passenger canview the display panel 5031 by stretching of the hinge portion 5032. Thedisplay panel 5031 has a function of displaying information by theoperation of the passenger.

Note that although bodies of a car and an airplane are shown as examplesof moving objects in this embodiment, this embodiment is not limitedthereto. The semiconductor devices can be provided to a variety ofobjects such as two-wheeled vehicles, four-wheeled vehicles (includingcars, buses, and the like), trains (including monorails, railroads, andthe like), and vessels.

This application is based on Japanese Patent Application serial no.2009-214848 filed with Japan Patent Office on Sep. 16, 2009, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: a firsttransistor; a second transistor; a third transistor; a fourthtransistor; a fifth transistor; and a sixth transistor, wherein a firstterminal of the first transistor is directly connected to a firstwiring, and a second terminal of the first transistor is directlyconnected to a second wiring, wherein a first terminal of the secondtransistor is directly connected to a third wiring, and a secondterminal of the second transistor is directly connected to the secondwiring, wherein a second terminal of the third transistor iselectrically connected to a gate of the first transistor, wherein afirst terminal of the fourth transistor is directly connected to thethird wiring, a second terminal of the fourth transistor is electricallyconnected to the gate of the first transistor, and a gate of the fourthtransistor is directly connected to a gate of the second transistor,wherein a first terminal of the fifth transistor is directly connectedto a fifth wiring, a second terminal of the fifth transistor is directlyconnected to the gate of the second transistor, and a gate of the fifthtransistor is directly connected to a sixth wiring, and wherein a firstterminal of the sixth transistor is directly connected to the thirdwiring, a second terminal of the sixth transistor is directly connectedto the gate of the second transistor, and a gate of the sixth transistoris directly connected to a fourth wiring.
 2. The semiconductor deviceaccording to claim 1, wherein the second terminal of the thirdtransistor is directly connected to a gate of the first transistor, andwherein the second terminal of the fourth transistor is directlyconnected to the gate of the first transistor.
 3. The semiconductordevice according to claim 1, wherein the third wiring is a first powerline, and wherein the fifth wiring is a second power line.
 4. Thesemiconductor device according to claim 1, wherein the first wiring is asignal line.
 5. A display device comprising: a controller; and a gatedriver electrically connected to the controller, the gate drivercomprising a semiconductor device according to claim
 1. 6. Thesemiconductor device according to claim 1, wherein a first terminal ofthe third transistor is electrically connected to the first wiring. 7.The semiconductor device according to claim 1, wherein a first terminalof the third transistor is electrically connected to a seventh wiringand a gate of the third transistor is electrically connected to thefourth wiring.
 8. The semiconductor device according to claim 1, whereina first terminal of the third transistor is electrically connected tothe fourth wiring and a gate of the third transistor is electricallyconnected to the fifth wiring.
 9. The semiconductor device according toclaim 1, wherein the first wiring is a first power supply line, whereinthe third wiring is a second power line, wherein the fifth wiring is athird power line, wherein the second wiring is a first signal line,wherein the fourth wiring is a second signal line, and wherein the sixthwiring is a third signal line.
 10. The semiconductor device according toclaim 1, wherein the fourth wiring is electrically connected to a shiftregister circuit.
 11. The semiconductor device according to claim 1,wherein the first to sixth transistors are transistors comprising anoxide semiconductor.
 12. An electronic appliance comprising thesemiconductor device according to claim
 1. 13. A semiconductor devicecomprising: a first transistor; a second transistor; a third transistor;a fourth transistor; a fifth transistor; and a sixth transistor, whereina first terminal of the first transistor is directly connected to afirst wiring, and a second terminal of the first transistor is directlyconnected to a second wiring, wherein a first terminal of the secondtransistor is directly connected to a third wiring, and a secondterminal of the second transistor is directly connected to the secondwiring, wherein a first terminal of the third transistor is directlyconnected to a fourth wiring and a second terminal of the thirdtransistor is electrically connected to a gate of the first transistor,wherein a first terminal of the fourth transistor is directly connectedto the third wiring, a second terminal of the fourth transistor iselectrically connected to the gate of the first transistor, and a gateof the fourth transistor is directly connected to a gate of the secondtransistor, wherein a first terminal of the fifth transistor is directlyconnected to a fifth wiring, a second terminal of the fifth transistoris directly connected to the gate of the second transistor, and a gateof the fifth transistor is directly connected to a sixth wiring, andwherein a first terminal of the sixth transistor is directly connectedto the third wiring, a second terminal of the sixth transistor isdirectly connected to the gate of the second transistor, and a gate ofthe sixth transistor is directly connected to the fourth wiring.
 14. Thesemiconductor device according to claim 13, wherein the second terminalof the third transistor is directly connected to a gate of the firsttransistor, and wherein the second terminal of the fourth transistor isdirectly connected to the gate of the first transistor.
 15. Thesemiconductor device according to claim 13, wherein the third wiring isa first power line, and wherein the fifth wiring is a second power line.16. The semiconductor device according to claim 13, wherein the firstwiring is a signal line.
 17. A display device comprising: a controller;and a gate driver electrically connected to the controller, the gatedriver comprising a semiconductor device according to claim
 13. 18. Thesemiconductor device according to claim 13, wherein a gate of the thirdtransistor is electrically connected to the fifth wiring.
 19. Thesemiconductor device according to claim 13, wherein the first wiring isa first power supply line, wherein the third wiring is a second powerline, wherein the fifth wiring is a third power line, wherein the secondwiring is a first signal line, wherein the fourth wiring is a secondsignal line, and wherein the sixth wiring is a third signal line. 20.The semiconductor device according to claim 13, wherein the fourthwiring is electrically connected to a shift register circuit.
 21. Thesemiconductor device according to claim 13, wherein the first to sixthtransistors are transistors comprising an oxide semiconductor.
 22. Anelectronic appliance comprising the semiconductor device according toclaim
 13. 23. A semiconductor device comprising: a first transistor; asecond transistor; a third transistor; a fourth transistor; a fifthtransistor; and a sixth transistor, wherein a first terminal of thefirst transistor is directly connected to a first wiring, and a secondterminal of the first transistor is directly connected to a secondwiring, wherein a first terminal of the second transistor is directlyconnected to a third wiring, and a second terminal of the secondtransistor is directly connected to the second wiring, wherein a firstterminal of the third transistor is directly connected to a gate of thethird transistor and a fourth wiring, a second terminal of the thirdtransistor is electrically connected to a gate of the first transistor,wherein a first terminal of the fourth transistor is directly connectedto the third wiring, a second terminal of the fourth transistor iselectrically connected to the gate of the first transistor, and a gateof the fourth transistor is directly connected to a gate of the secondtransistor, wherein a first terminal of the fifth transistor iselectrically connected to a fifth wiring, a second terminal of the fifthtransistor is directly connected to the gate of the second transistor,and a gate of the fifth transistor is directly connected to a sixthwiring, and wherein a first terminal of the sixth transistor is directlyconnected to the third wiring, a second terminal of the sixth transistoris directly connected to the gate of the second transistor, and a gateof the sixth transistor is electrically connected to the fourth wiring.24. The semiconductor device according to claim 23, wherein the firstterminal of the fifth transistor is directly connected to the fifthwiring, and wherein the gate of the sixth transistor is directlyconnected to the fourth wiring.
 25. The semiconductor device accordingto claim 23, wherein the third wiring is a first power line, and whereinthe fifth wiring is a second power line.
 26. The semiconductor deviceaccording to claim 23, wherein the first wiring is a signal line. 27.The semiconductor device according to claim 23, wherein the fifth wiringis a signal line.
 28. A display device comprising: a controller; and agate driver electrically connected to the controller, the gate drivercomprising a semiconductor device according to claim
 23. 29. Thesemiconductor device according to claim 23, wherein the first wiring isa first power supply line, wherein the third wiring is a second powerline, wherein the fifth wiring is a third power line, wherein the secondwiring is a first signal line, wherein the fourth wiring is a secondsignal line, and wherein the sixth wiring is a third signal line. 30.The semiconductor device according to claim 23, wherein the fourthwiring is electrically connected to a shift register circuit.
 31. Thesemiconductor device according to claim 23, wherein the first to sixthtransistors are transistors comprising an oxide semiconductor.
 32. Anelectronic appliance comprising the semiconductor device according toclaim 23.